[core] Align BIGINT and timestamp schema evolution with Java

[JingsongLi]

What is the purpose of the change?

Align the existing BIGINT/timestamp schema-evolution paths with Java casts. PyPaimon already reads these type changes, but Arrow's generic cast interprets timestamps as physical ticks: for example 42001ms becomes BIGINT 42001, while Java returns epoch seconds 42.

Brief change log

• Convert TIMESTAMP and TIMESTAMP_LTZ to BIGINT using epoch seconds and floor division for pre-epoch values.
• Match Java's LTZ Timestamp local-date-time round trip, including its int epoch day.
• Move the existing numeric-to-ordinary-TIMESTAMP conversion into the shared evolution cast module and apply Java signed-long wrapping to the intermediate seconds * 1000 milliseconds. Preserve lenient NULLs when Arrow's target unit cannot represent the result.
• Reuse recursive evolution and predicate/statistics paths without adding a public API or dependency.
• Cover Arrow units, slices, NULLs, Java boundary outputs, nullable ROW/ARRAY/MAP values, and mixed old/new files with predicates and projection across append, primary-key and data-evolution tables.

Verifying this change

• Reproduced the old timestamp-to-BIGINT unit error in both the core test and a REST Native integration test.
• cargo test -p paimon --lib arrow::: 522 passed, 1 ignored; after adding the final nullable-container test, all 28 nested-evolution tests passed.
• cargo test -p paimon --test schema_evolution_cast_test: 2 passed (each covers append, PK and data evolution).
• cargo +1.98.0 fmt --all -- --check
• cargo +1.98.0 clippy --locked --all-targets --workspace --features fulltext,vortex -- -D warnings
• Java CastExecutorTest#testTimestampToNumeric+testTimestampToNumericPreEpoch: 2 passed. Direct calls to Java CastExecutors also confirmed the long-wrapping and extreme-LTZ golden values.
• Rebuilt the Python extension from this branch: 166 focused Python schema-evolution tests, 112 existing read/projection tests, and final MAP key projection checks passed.

The accompanying PyPaimon PR apache/paimon#10508 aligns its existing Python casts with Java and adds Native REST parity coverage. This only addresses type-change paths already supported by Python.

[leaves12138]

The Rust implementation aligns the BIGINT/timestamp evolution paths with Java, including floor division, LTZ round-trip behavior, signed-long wrapping, nested values, and statistics/predicate safety. The focused Rust tests and CI are green.