Fix BulkUpdate truncating datetime binds to whole seconds

[blurvene]

Problem

PgSqlCaller::BulkUpdate#bindings encoded each column's value array with
typecast_array(values, type: <symbol>), which rebuilds the type via
ActiveRecord::Type.lookup(:datetime, array: true) — a generic, non-adapter
type whose PG array text encoder formats Time elements with Time#to_s,
i.e. whole seconds:

  typecast_array(:datetime) → "{\"2026-06-22 16:15:08 UTC\"}"   # .193 dropped
  column-bound serialize     → "2026-06-22 16:15:08.193 UTC"

Two consequences:

• SET writes stored timestamps truncated to the second.
• unique_by matches on a timestamp column built WHERE ts = '…:08'
  (.000), which never equals a stored sub-second row → zero rows matched,
  silent no-op (no error, returns 0).

Not a precision-of-type issue and not a timezone shift — AR's own
where/insert_all and the scalar serialize keep precision (connection-bound
quoting); only the array encoding path was lossy.

Fix

bindings now routes datetime/time columns through precise_temporal_array,
formatting each value to a full-microsecond literal (%Y-%m-%d %H:%M:%S.%6N%z,
normalized to UTC — correct for both timestamp and timestamptz). The existing
?::<sql_type>[] cast reparses it losslessly. Non-temporal columns are unchanged.

Tests

• Exact sub-second round-trip (the existing datetime test used be_within(1),
  which masked the bug).
• unique_by match on a sub-second datetime key.

Both verified red without the fix, green with. Full suite: 65 examples, 0 failures.

Compatibility

Bug fix only, no API change. Bumped to 1.1.1.

[Copilot]

Pull request overview

Fixes PgSqlCaller::BulkUpdate losing sub-second precision when binding datetime/time column arrays, which could both truncate stored timestamps and cause unique_by matches on sub-second keys to miss rows.

Changes:

• Route temporal columns through a custom array-literal encoder that preserves microseconds.
• Tighten specs to assert exact microsecond preservation and unique_by matching on sub-second datetimes.
• Bump gem version to 1.1.1 and document the fix in CHANGELOG.md.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
lib/pg_sql_caller/bulk_update.rb	Adds temporal-aware array encoding to preserve microsecond precision for datetime/time binds.
spec/pg_sql_caller/bulk_update_spec.rb	Adds regression specs for microsecond round-trip and unique_by matching on sub-second datetimes.
lib/pg_sql_caller/version.rb	Bumps version from 1.1.0 to 1.1.1.
CHANGELOG.md	Adds a 1.1.1 entry describing the temporal array precision fix.

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