chore: rename subscribe_batch to subscribe_buckets

[luoyuxia]

Purpose

Linked issue: close #253

Brief change log

Tests

API and Format

Documentation

[luoyuxia]

@fresh-borzoni Please help review it.

[Copilot]

Pull request overview

This PR renames the method subscribe_batch to subscribe_buckets across the Rust codebase and C++ bindings to avoid confusion with "record batch" terminology. The change improves API clarity by ensuring that "batch" terminology is reserved for record batches rather than collections of bucket subscriptions.

Changes:

• Renamed subscribe_batch method to subscribe_buckets in scanner implementation and public APIs
• Updated error messages to reflect the new method name
• Updated all call sites in tests, examples, and C++ bindings

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/fluss/tests/integration/log_table.rs	Updated test to use the renamed subscribe_buckets method
crates/fluss/src/client/table/scanner.rs	Renamed internal and public subscribe_batch methods to subscribe_buckets in LogScannerInner, LogScanner, and RecordBatchLogScanner, including error message update
bindings/cpp/src/table.cpp	Updated C++ binding to call the renamed subscribe_buckets FFI method
bindings/cpp/src/lib.rs	Renamed FFI bridge methods from subscribe_batch to subscribe_buckets
bindings/cpp/examples/example.cpp	Updated example code error check string to reference subscribe_buckets

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[fresh-borzoni]

@luoyuxia TY for the PR. LGTM. I'll rename in python bindings as well then.