Improve datetime parsing for loose timestamp formats

[Ahamed1846]

Improve datetime parsing for loose timestamp formats (#5060)

Fixes #5060

This PR enhances date/time parsing so that Mathesar correctly handles valid timestamp inputs that omit leading zeros or seconds. Previously, entries such as "2000-01-01 9:00:00" or "2000-01-01 09:00" were not parsed and were sent to PostgreSQL unchanged, causing unexpected timezone shifts.

Technical details

Problem

parseWithSpec matched only strict timestamp formats and rejected variants without leading zeros or without seconds. When parsing failed, the unparsed string was sent directly to PostgreSQL, resulting in incorrect values for timestamptz columns.

Fix

Additional timestamp format variants were included in
DateTimeSpecification so that:

• Hours without leading zero (H:mm:ss, H:mm)
• Timestamps without seconds (YYYY-MM-DD HH:mm)
• Timestamps using single-digit hour (YYYY-MM-DD H:mm:ss)

are now correctly parsed and converted to canonical form.

Behavior Changes

• Valid timestamp inputs with missing leading zeros now parse correctly.
• Values are consistently normalized before being sent to the backend.
• No changes were made to date-only parsing or time-only behavior.

Files touched

• mathesar_ui/src/utils/date-time/DateTimeSpecification.ts
• mathesar_ui/src/utils/date-time/DateTimeFormatter.ts

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  visible errors.

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