fix: don't crash parseDate when dateFormat contains timezone tokens

[xianjianlf2]

Description

Linked issue: #6303

Problem
When dateFormat contains a timezone token (e.g. "MMMM d, yyyy h:mm aa (zzz)"), typing anything into the datepicker input crashes the page. date-fns parse() throws a RangeError ("Format string contains an unescaped latin alphabet character z") because z/zzz are format-only tokens that parse cannot consume. The error propagates out of parseDate into handleChange, so the component throws and the user's typed input is lost.

Changes

• src/date_utils.ts: wrapped the date-fns parse() call inside parseDate's format loop in a try/catch. When parse throws on an unparseable token, the loop continues, so parsing falls through to the existing native Date fallback (when strictParsing is false) instead of crashing. Behavior for all parseable formats is unchanged.
• src/test/date_utils_test.test.ts: added a regression test that parses "July 6, 2026 3:30 PM (GMT+0)" against "MMMM d, yyyy h:mm aa (zzz)", asserting parseDate does not throw and the date/time still resolves via the native Date fallback.

Screenshots

N/A (no visual changes)

To reviewers

zzz renders fine through formatDate (date-fns format supports it), so users legitimately configure it in dateFormat; only the parsing path threw. The try/catch also covers any other format-only token parse rejects.

Test run: yarn jest src/test/date_utils_test.test.ts — 236 passed. Prettier and ESLint pass on the touched files.

Fixes #6303

Contribution checklist

• I have followed the contributing guidelines.
• I have added sufficient test coverage for my changes.
• I have formatted my code with Prettier and checked for linting issues with ESLint for code readability.