Function parseTimezoneOffsetToMinutes

parseTimezoneOffsetToMinutes(str: string): Maybe<number>
Parse a timezone offset string to offset minutes.

Accepts multiple formats:
- ISO 8601: "+08:00", "-05:30", "Z"
- Luxon format: "UTC+8", "GMT-5"
- UTC variants: "UTC", "GMT", "Zulu"
Supports seconds for archaic offsets like "-00:25:21" (Ireland 1880-1916).

Note: Does NOT validate that the offset is a real-world timezone offset. Use validTzOffsetMinutes for validation.
Parameters
- str: string
  Timezone offset string
Returns Maybe<number>
Offset in minutes, or undefined if invalid
Example
```
parseTimezoneOffsetToMinutes("+08:00")     // 480
parseTimezoneOffsetToMinutes("UTC-5")      // -300
parseTimezoneOffsetToMinutes("Z")          // 0
parseTimezoneOffsetToMinutes("-00:25:21")  // -25.35 (archaic Ireland)
parseTimezoneOffsetToMinutes("invalid")   // undefined
```
- Defined in src/Timezones.ts:439