refactor(store)!: simplify store interface and improve tests (#104)

BREAKING CHANGES:
- Remove `get_size()` method from IpldStore trait and replace with `get_block_count()`
- Remove PlaceholderStore implementation
- Make `is_empty()` a default implementation based on block count
- Rename MemoryStore::new to MemoryStore::with_chunker_and_layout

Changes:
- Improve test coverage for MemoryStore with more focused test cases
- Update ASCII diagram documentation for FlatLayout
- Add workspace-level tempfile dependency
- Update tempfile to 3.15.0
- Add hex and libipld dependencies to monofs

Cargo.toml

@@ -51,6 +51,7 @@ monoutils-store = { version = "0.2", path = "./monoutils-store" }
 monoutils = { version = "0.2", path = "./monoutils" }
 chrono = { version = "0.4", features = ["serde"] }
 criterion = "0.5"
+tempfile = "3.15"
 test-log = "0.2"
 typed-path = "0.10"
 toml = "0.8"

monocore/Cargo.toml

@@ -48,7 +48,7 @@ serde_json.workspace = true
 sha2.workspace = true
 signal-hook = "0.3.17"
 structstruck.workspace = true
-tempfile = "3.14.0"
+tempfile.workspace = true
 thiserror.workspace = true
 tokio.workspace = true
 toml.workspace = true

monofs/Cargo.toml

@@ -29,3 +29,6 @@ serde_json.workspace = true
 monoutils.workspace = true
 serde_ipld_dagcbor.workspace = true
 pretty-error-debug.workspace = true
+libipld.workspace = true
+hex.workspace = true
+tempfile.workspace = true