docs: explain date_bin daylight saving behavior

[Prajwal-k-tech]

Which issue does this PR close?

• Closes Document that date_bin with an explicit origin drifts an hour across a DST transition #25168

Rationale for this change

An explicit date_bin origin anchors buckets to an instant. For timezone-aware timestamps, an origin aligned with local midnight can therefore move to 01:00 after a daylight saving transition. The issue confirms this behavior matches PostgreSQL and DuckDB; the missing piece is documenting the tradeoff and the local-time alternatives.

What changes are included in this PR?

• Clarify that date_bin uses a fixed origin and does not adjust it for daylight saving changes.
• Point users to date_trunc for calendar units and to to_local_time for binning other intervals against local wall-clock boundaries.
• Regenerate the SQL scalar-function reference from the canonical function documentation.

This PR was prepared with AI assistance. The source change, generated reference, issue reproductions, and project checks were reviewed for consistency.

What is the testing strategy for this PR?

This is a documentation-only change, so no runtime tests were added. Verified generated docs with ./dev/update_function_docs.sh and ./ci/scripts/check_generated_docs.sh; also ran cargo +1.99.0 fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings, ./ci/scripts/doc_prettier_check.sh --write --allow-dirty, and git diff --check.

Are there any user-facing changes?

Yes. The date_bin reference now explains fixed-origin behavior across DST and documents alternatives for local calendar boundaries.

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