Localize time formatting with Intl.DateTimeFormat

[borisgraeff-pxo]

Why

Time strings generated by toText were always formatted with an English-style 12-hour clock (AM/PM), even when the specified locale was not English.
This PR makes time rendering locale-aware so generated recurrence descriptions are consistent with the selected language.

What Changed

• Reworked time formatting in src/totext.ts to use Intl.DateTimeFormat with the resolved locale.
• Updated formatTime to:
  • accept the rule timezone context (Temporal.ZonedDateTime),
  • format hour / minute / second combinations through Intl,
  • preserve timezone-aware output.
• Updated timezone label extraction (tzAbbreviation) to use locale-aware Intl.DateTimeFormat fallback behavior.
• Adjusted toText time rendering path to pass locale + timezone context when formatting byHour / byMinute / bySecond.

Tests

Updated i18n expectations in:

• src/tests/totext.i18n.test.ts
• src/tests/totext.i18n.extra.test.ts

Expected outputs now reflect locale-specific time conventions:

• 24h style where applicable (e.g. 17:30 instead of 5:30 PM)
• locale-specific day periods and timezone naming (e.g. GMT-4, localized variants instead of fixed EDT/CST)

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