feat: expose branch_identifier in python and java bindings

[majin1102]

Motivation

• Surface the full branch lineage (version -> uuid mapping) from Rust BranchIdentifier into higher-level bindings so clients can inspect a branch's lineage chain.

Description

• Update the JNI layer (java/lance-jni/src/blocking_dataset.rs) to construct and pass a List<BranchVersionMapping> when creating the Java Branch object.
• Extend the Java model (java/src/main/java/org/lance/Branch.java) with an inner BranchVersionMapping class, add a branchIdentifier field and getter, update constructor/signature, and include it in toString, equals, and hashCode.
• Update Java tests (java/src/test/java/org/lance/DatasetTest.java) to assert the presence and contents of branchIdentifier for created branches.
• Add branch_identifier: List[Tuple[int, str]] to the Python Branch TypedDict (python/python/lance/dataset.py) and update the Python Rust bridge (python/src/dataset.rs) to include meta.identifier.version_mapping in the returned branch dictionaries.
• Update Python tests (python/python/tests/test_dataset.py) to validate the branch_identifier contents in branches.list() responses.

Testing

• Ran the modified Java unit test DatasetTest::test_branches which exercises branch creation, listing and metadata assertions, and it passed.
• Ran the modified Python test test_branches with pytest which verifies branch_identifier in branches.list() and it passed.
• Exercised JNI/bridge code paths while running the above tests to validate interop and serialization of the version->uuid mappings, and no failures were observed.

[github-actions]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve the previous Branch constructor overload

This change removes the only public Branch(String, String, long, long, int) constructor and replaces it with a new signature that requires List<BranchVersionMapping>, which is a source/binary incompatible API break for downstream Java users who instantiate Branch directly. After upgrading, existing callers will fail to compile (or hit NoSuchMethodError when artifacts are mixed). Please keep the old constructor as an overload and delegate to the new one with a default lineage list to maintain compatibility.

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[chatgpt-codex-connector]

Avoid unstable lineage IDs in Branch equality

Including branchIdentifier in equals makes equality unstable for legacy branches whose refs JSON lacks identifier: Rust fills that with BranchIdentifier::none(), which generates a fresh UUID during deserialization, so the same logical branch can compare unequal across separate branches().list() calls. This can break client-side map/set lookups and cache keys for older datasets; consider excluding this field from equality (or ensuring legacy identifiers are deterministic before exposing them).

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[jackye1995]

looks good to me!