fix: rewrite ordered timestamp widening predicates

[discord9]

Which issue does this PR close?

• N/A — issues are disabled in this fork.

Rationale for this change

GreptimeDB metric timestamps use millisecond precision while now() returns a nanosecond timestamp. After mixed-timestamp coercion began preserving the finer precision, predicates such as:

CAST(ts_ms AS Timestamp(ns)) >= TimestampNanosecond(1784895098272960878)

could no longer be unwrapped when the target literal was not aligned to the source timestamp unit. The residual cast prevents native timestamp predicate pushdown.

Although a non-aligned target literal has no singleton value preimage, ordered comparisons have exact source-domain bounds. For example, the predicate above is equivalent under the fork's existing timestamp-widening overflow policy to:

ts_ms >= TimestampMillisecond(1784895098273)

What changes are included in this PR?

• Add an ordered timestamp-widening fallback after the existing exact cast-preimage path.
• Compute source bounds with Euclidean floor/ceil arithmetic using i128:
  • >= L and < L use ceil(L / q).
  • > L and <= L use floor(L / q).
• Support all timestamp precision-widening unit pairs with matching timezones.
• Keep non-aligned equality, distinctness, and IN predicates unchanged.
• Cover logical and physical rewrites, CAST/TRY_CAST, literal-left operator swaps, negative timestamps, and i64 boundaries.

This change deliberately follows the fork's existing timestamp-widening overflow policy. It does not claim full-domain equivalence for extreme source values whose regular CAST would overflow or whose TRY_CAST would produce NULL.

Are these changes tested?

Yes:

cargo test -p datafusion-expr-common test_cast_predicate_preimage_timestamp_widening
cargo test -p datafusion-optimizer test_cast_preimage_timestamp_widening
cargo test -p datafusion-physical-expr timestamp_widening
cargo fmt --all -- --check
cargo clippy -p datafusion-expr-common -p datafusion-optimizer -p datafusion-physical-expr --all-targets -- -D warnings
git diff --check

Are there any user-facing changes?

Yes. Ordered comparisons over timestamp precision-widening casts can now remove the column-side cast for non-aligned literals, enabling predicate pushdown while preserving the comparison boundary within the existing overflow policy. There is no SQL syntax or public API change.

[WenyXu]

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[chatgpt-codex-connector]

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