fix: reject date-time/time strings with trailing characters (#2572)

[veeceey]

Fixes #2572

The validTimestamp runtime in lib/runtime/timestamp.ts already correctly rejects date-time and time strings that have trailing characters after the timezone (e.g. 2024-06-01T12:34:56ZAS, 12:34:56+12:44AS). The TIME regex's $ anchor ensures no extra characters are accepted.

This PR adds regression tests that explicitly cover the cases from the issue:

• Trailing characters after Z timezone indicator (2024-06-01T12:34:56ZAS)
• Trailing characters after offset (2024-06-01T12:34:56+12:44AS)
• Leading whitespace or characters
• End-to-end JTD timestamp validation for these cases

Tests verified locally:

  Invalid date-time and time with trailing characters (issue #2572)
    validTimestamp runtime
      ✔ should reject date-time strings with trailing characters after Z
      ✔ should reject date-time strings with trailing characters after offset
      ✔ should reject date-time strings with leading whitespace or characters
      ✔ should accept valid date-time strings
      ✔ should accept valid date strings when allowDate is true
      ✔ should reject invalid date strings when allowDate is true
    JTD timestamp validation end-to-end
      ✔ should reject timestamps with trailing characters after Z
      ✔ should reject timestamps with trailing characters after offset

  8 passing (2ms)