Regression tests for [JsonPropertyName] on temporal types (closes #4253)

[jeremydmiller]

Closes #4253

Summary

The issue reported that [JsonPropertyName("ts")] on a DateTimeOffset property is ignored by Marten's LINQ provider — SQL emits (data ->> 'Timestamp') instead of (data ->> 'ts'), and CREATE INDEX DDL has the same issue.

After tracing the code paths on master (8.30.0), the obvious candidates all look correct:

• QueryableMember base ctor sets RawLocator using member.ToJsonKey(casing) which honors [JsonPropertyName]
• DateTimeOffsetMember, DateTimeMember, DateOnlyMember, TimeOnlyMember all inherit this base behavior
• ComputedIndex resolves members through the same MemberFor path as LINQ

I wrote 8 regression tests mirroring the bug repro exactly. All 8 pass on master — the bug does not reproduce on the current code. The reporter may have been on an older build, or there's a reproduction step I'm missing.

Rather than keep the issue open without a reproducible repro, landing these regression tests to prevent future regressions across all temporal types.

Tests added

LINQ Where SQL (src/LinqTests/Acceptance/json_naming_attributes.cs):

• recognize_stj_json_property_on_datetimeoffset_in_linq
• recognize_stj_json_property_on_datetimeoffset_required_init_in_linq — uses the required { get; init; } shape from the bug report
• recognize_stj_json_property_on_datetime_in_linq
• recognize_stj_json_property_on_dateonly_in_linq
• recognize_stj_json_property_on_timeonly_in_linq
• end_to_end_query_with_datetimeoffset_json_property_name — end-to-end count query from the bug repro

Index DDL (src/DocumentDbTests/Indexes/computed_indexes.cs):

• datetimeoffset_index_ddl_uses_json_property_name
• datetimeoffset_required_init_index_ddl_uses_json_property_name

Test plan

• All 6 LINQ tests pass on master (net9.0)
• Both index DDL tests pass on master (net9.0)
• End-to-end integration test with real PostgreSQL passes

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