feat(chunkv5): Chunk V5 structure, encoding and decoding

pkg/chunkenc/chunk-v5.md

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+# Organized Chunk Format Documentation (WIP)
+## Overview
+
+The organized chunk format (represented by the format version V5/ChunkFormatV5) is a new storage format that separates log lines, timestamps, and structured metadata into distinct sections within a chunk to enable more efficient querying. This format aims to improve performance by organizing data in a way that minimizes unnecessary decompression when only specific fields are needed.
+
+## Block Structure Diagram
+
+```
+┌─────────────────────────────────────────────┐
+│               Chunk Format V5               │
+├─────────────────────────────────────────────┤
+│ Magic Number (4 bytes)                      │
+│ Format Version (1 byte)                     │
+│ Encoding Type (1 byte)                      │
+├─────────────────────────────────────────────┤
+│                                             │
+│ Structured Metadata Section                 │
+│ ┌─────────────────────────────────────┐    │
+│ │ Length                              │    │
+│ │ Compressed Metadata Symbols         │    │
+│ │ Checksum                           │    │
+│ └─────────────────────────────────────┘    │
+│                                             │
+│ Log Lines Section                          │
+│ ┌─────────────────────────────────────┐    │
+│ │ Length                              │    │
+│ │ Compressed Log Lines                │    │
+│ │ Checksum                           │    │
+│ └─────────────────────────────────────┘    │
+│                                             │
+│ Timestamps Section                         │
+│ ┌─────────────────────────────────────┐    │
+│ │ Length                              │    │
+│ │ Compressed Timestamps               │    │
+│ │ Checksum                           │    │
+│ └─────────────────────────────────────┘    │
+│                                             │
+│ Block Metadata Section                      │
+│ ┌─────────────────────────────────────┐    │
+│ │ Number of Blocks                    │    │
+│ │ Block Entry Count                   │    │
+│ │ Min/Max Timestamps                  │    │
+│ │ Offsets & Sizes                    │    │
+│ │ Checksum                           │    │
+│ └─────────────────────────────────────┘    │
+│                                             │
+│ Section Offsets & Lengths                  │
+└─────────────────────────────────────────────┘
+```
+
+## Section Details
+
+1. **Header**
+   - Magic Number (4 bytes): Identifies the chunk format
+   - Format Version (1 byte): Version 5 for organized format
+   - Encoding Type (1 byte): Compression type used
+
+2. **Structured Metadata Section**
+   - Contains label key-value pairs for each log entry
+   - Compressed using the specified encoding
+   - Includes length and checksum
+   - Uses symbol table for efficient storage of repeated strings
+
+3. **Log Lines Section**
+   - Contains the actual log message content
+   - Compressed independently
+   - Includes length and checksum
+
+4. **Timestamps Section**
+   - Contains entry timestamps
+   - Compressed independently
+   - Includes length and checksum
+
+5. **Block Metadata Section**
+   - Number of blocks in the chunk
+   - Entry counts per block
+   - Min/Max timestamps per block
+   - Offsets and sizes for each block
+   - Checksum for integrity verification
+
+6. **Section Offsets & Lengths**
+   - End of chunk contains offsets and lengths for each major section
+   - Enables quick navigation to specific sections
+
+## Query Plan
+
+The organized format enables optimized query patterns:
+
+1. **Label Queries**
+   - Can decompress only the structured metadata section
+   - Avoids decompressing log lines and timestamps
+   - Efficient for label-based filtering
+
+2. **Timestamp-Based Queries**
+   - Can read only timestamps section first
+   - Enables efficient time range filtering before accessing log content
+   - Reduces unnecessary decompression of log lines
+
+3. **Content Queries**
+   - For full text search or parsing
+   - Decompresses log lines section
+   - Can correlate with timestamps and metadata as needed
+
+### Query Optimization Flow
+
+```
+┌──────────────────┐
+│  Query Request   │
+└────────┬─────────┘
+         │
+         v
+┌──────────────────┐
+│  Analyze Query   │
+│    Components    │
+└────────┬─────────┘
+         │
+         v
+┌──────────────────┐   Yes   ┌─────────────────┐
+│ Label Filtering? ├────────>│ Read Metadata   │
+└────────┬─────────┘        └────────┬────────┘
+         │ No                        │
+         v                           v
+┌──────────────────┐         ┌─────────────────┐
+│  Time Filtering? │         │  Apply Label    │
+└────────┬─────────┘         │   Filters       │
+         │                   └────────┬────────┘
+         v                           │
+┌──────────────────┐                │
+│   Read Lines     │                │
+└────────┬─────────┘                │
+         │                          │
+         v                          v
+┌──────────────────────────────────────────┐
+│            Combine Results               │
+└──────────────────────────────────────────┘
+```
+
+## Implementation Notes
+
+The implementation is handled through several key components:
+
+1. **Block Organization**
+   - `organisedHeadBlock` struct manages the organization of data during writes
+   - Maintains separate buffers for lines, timestamps, and metadata
+
+2. **Iterator Implementation**
+   - `organizedBufferedIterator` provides efficient access to the organized format
+   - Can selectively decompress only needed sections
+   - Maintains separate readers for each section
+
+3. **Compression**
+   - Each section can be compressed independently
+   - Enables optimal compression for different types of data
+   - Supports various compression algorithms through the `compression.Codec` interface
+
+## Benefits
+
+1. **Reduced I/O**
+   - Selective decompression of only needed sections
+   - More efficient use of memory and CPU
+
+2. **Better Compression Ratios**
+   - Similar data types grouped together
+   - More effective compression within sections
+
+3. **Query Flexibility**
+   - Optimized access patterns for different query types
+   - Better performance for label and time-based queries
+
+4. **Maintainability**
+   - Clear separation of concerns
+   - Easier to extend and modify individual sections
+