feat: LQL timestamp support for unix timestamps and ISO8601

[msmithstubbs]

Add support for LQL timestamp filters in these formats:

Unix timestamp

Use Unix timestamps as 10-digit seconds, 13-digit milliseconds, or 16-digit microseconds.
Microsecond values are truncated to milliseconds.
Unix timestamps are interpreted as UTC.

Examples:

• t:>=1710683222000
• t:<=1710683222000000
• t:1710683222..1710683822
• t:1710683222000..1710683822000

ISO8601 format

A timestamp can be written as:

1. A date, such as YYYY-MM-DD
   This is interpreted in the user’s selected timezone.
2. A datetime with a Z suffix
   This is treated as a UTC datetime.
3. A datetime with an explicit timezone offset
   This is treated using the supplied offset.

Examples:

• t:2026-03-17..2026-03-19
• t:>2026-03-17T14:47:02Z
• t:>=2026-03-17T14:47:02.123Z
• t:<2026-03-17T14:47:02+02:00
• t:>=2026-03-17T14:47:02-02:00
• t:2026-03-17T14:47:02+02:00..2026-03-17T15:47:02+02:00