[TASK-191] Arrow serialization for decimal and temporal types

[fresh-borzoni]

closes #191

Enables Arrow serialization for decimal and temporal types, providing feature parity with the Java client.

Fluss Type	Arrow Type
DECIMAL(p, s)	Decimal128(p, s)
DATE	Date32
TIME	Time32/Time64
TIMESTAMP	Timestamp (all precisions)
TIMESTAMP_LTZ	Timestamp (all precisions)

[fresh-borzoni]

@luoyuxia @leekeiabstraction PTAL 🙏

[Copilot]

Pull request overview

Enables Apache Arrow serialization for Fluss DECIMAL and temporal types (DATE, TIME, TIMESTAMP, TIMESTAMP_LTZ) to match feature parity with the Java client.

Changes:

• Added Arrow schema/type mappings for decimal and temporal Fluss types and made schema conversion fallible (Result).
• Implemented Arrow appends for decimal/date/time/timestamps, including decimal rescaling/validation and timestamp unit handling.
• Updated write/batch/scanner codepaths and tests to propagate the new fallible APIs.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/fluss/src/row/datum.rs	Adds datum accessors/conversions and Arrow append support for decimal + temporal types.
crates/fluss/src/record/arrow.rs	Extends Arrow schema/type mapping and RecordBatch builder creation for decimal/temporal Arrow types; propagates errors instead of panicking.
crates/fluss/src/client/write/batch.rs	Makes Arrow write batch construction fallible to reflect schema/builder validation.
crates/fluss/src/client/write/accumulator.rs	Propagates new Result return from Arrow write batch creation.
crates/fluss/src/client/table/scanner.rs	Propagates fallible Arrow schema conversion when initializing scanners/read contexts.
crates/fluss/src/client/table/log_fetch_buffer.rs	Updates tests/helpers to handle fallible Arrow schema conversion and builder creation.

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[leekeiabstraction]

TY for the PR! Left some comments

[leekeiabstraction]

Added further question

[luoyuxia]

@fresh-borzoni Thanks for the pr. LGTM overall, only lefr minor comments.

[fresh-borzoni]

@leekeiabstraction @luoyuxia
Thanks for the review. Addressed the comments. PTAL 🙏

[luoyuxia]

@fresh-borzoni Thanks. LGTM!