feat(transcode): round-4 Date(Month) and Date(Year) precision support

[AdaWorldAPI]

Summary

Closes the deferred item from PR #316: parse_iso_date_to_days previously only accepted YYYY-MM-DD, even when the column was declared Date(Month) or Date(Year). Round-4 widens the parser to accept all three precisions, treating lower-precision inputs as the earliest point in the period:

Input	Interpreted as	Days since epoch
YYYY-MM-DD	exact day	(Hinnant)
YYYY-MM	first day of the month	1970-02 → 31
YYYY	first day of the year	2000 → 10_957

Algorithm itself unchanged (Howard Hinnant civil_to_days). The match parts.as_slice() lets the parser default the missing components without changing the math.

Tests (5 new + 1 expanded; 13 typed_resolver total)

• typed_resolver_iso_year_only_parses_to_jan_1
• typed_resolver_iso_year_month_parses_to_day_1
• typed_resolver_iso_lower_precision_rejects_bad_components — bad month / bad day / non-numeric / empty year
• typed_resolver_iso_lower_precision_handles_leap_year_feb — 2020-02 = day 31 of 2020 = 18_293 since epoch
• typed_resolver_iso_date_rejects_garbage (expanded) — adds empty-string + 4-part-input rejection cases

13/13 typed_resolver tests pass under query-lite,auth-rls-lite. Clippy clean, fmt clean.

What's still deferred (round-5 territory)

• Strict-mode parser that REFUSES cross-precision inputs (e.g. a column declared Date(Day) rejects a YYYY-only string). Today's permissive default is the right round-1 choice for graceful up-cast; strict-mode lands when a consumer asks.
• Date(DateTime) precision — ISO timestamp parser would need a Timestamp column type, not Date32. Different Arrow plumbing.

Cross-link

• PR feat(transcode): round-3 typed-value resolver for triples_to_batch #316 (round-3 typed-value resolver, where this was deferred)
• PR feat(transcode): Phase-2-B triples_to_batch (ExpandedTriple stream → RecordBatch) #313 (round-1 triples_to_batch, where Date(_) was first plumbed)

Test plan

• cargo test transcode::zerocopy::tests::typed_resolver — 13/13 pass
• cargo clippy --all-targets --features query-lite,auth-rls-lite -- -D warnings
• cargo fmt --check

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