Feat: Support creating multiple files with single --parts command

[prantogg]

This PR introduces the following changes:

1. Running a command like this will automatically create 10 files for each large table (in parallel)

   spatialbench-cli -s 100 --parts=10

2. When --parts option is specified, each table is written out to output_dir/table/table.part.extension

   /sf1-parquet/trip/trip.1.parquet
   /sf1-parquet/trip/trip.2.parquet
   

3. If the target output file already exists, then it will not be regenerated. This allows you to kill an instance of tpchgen-cli and then run the same command to pick back up where it left off
4. Atomic file generation - spatialbench-cli writes to a file named ".inprogress" and when complete renames the file
5. Refactors Zone table generation code for better readability

[Copilot]

Pull Request Overview

This PR introduces support for generating multiple partitioned files with a single --parts command, along with atomic file generation and improved Zone table code organization.

Key Changes:

• Automatic generation of multiple partitioned files when --parts is specified without --part
• Files written to output_dir/table/table.part.extension structure when partitioned
• Atomic file generation using temporary .inprogress files with rename on completion
• Skip regeneration if target file already exists

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tools/generate_data.py	Simplified by removing staging directory logic, now delegates partitioning to spatialbench-cli
spatialbench-cli/tests/cli_integration.rs	Added comprehensive tests for no-overwrite behavior and multi-part generation
spatialbench-cli/src/zone_df.rs	Removed monolithic zone generation file
spatialbench-cli/src/zone/writer.rs	New module handling atomic parquet file writing with skip-if-exists logic
spatialbench-cli/src/zone/transform.rs	New module for zone data SQL transformations
spatialbench-cli/src/zone/stats.rs	New module for zone table statistics and row group calculations
spatialbench-cli/src/zone/partition.rs	New module implementing partition strategy and batch slicing
spatialbench-cli/src/zone/mod.rs	New module orchestrating single and multi-part zone generation
spatialbench-cli/src/zone/main.rs	New entry point for zone generation with format handling
spatialbench-cli/src/zone/datasource.rs	New module for DataFusion context setup and remote data loading
spatialbench-cli/src/zone/config.rs	New module for zone generation configuration
spatialbench-cli/src/runner.rs	New parallel execution engine with thread pooling for generation plans
spatialbench-cli/src/plan.rs	Enhanced with partitioning support and chunk count tracking
spatialbench-cli/src/output_plan.rs	New module for output file planning and directory management
spatialbench-cli/src/main.rs	Refactored to use new runner architecture and output planning
README.md	Updated with simplified partitioned output example

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[jiayuasu]

LGTM. In another PR, can you add the detailed usage to here? https://sedona.apache.org/spatialbench/datasets-generators/ The README is too long now.