Update boa_temporal Time Zone design

[nekevss]

The updates on this branch is to bring the time zone implementation in line with the design from #3522 and related to #1804.

It changes the following:

• Changes TimeZoneSlot to the below

pub enum TimeZoneSlot<Z: TzProtocol> {
    /// A native `TimeZone` representation.
    Tz(TimeZone),
    /// A Custom `TimeZone` that implements the `TzProtocol`.
    Protocol(Z),
}

• Adds the custom time zone object (with a Trace impl).

Notably, as further context on the below, Time Zones right now is mostly the structure/scaffolding with limited functionality. We'll need to figure out a good way to handle tz system calls and IANA mapping (whether that be using some icu4x provider or baking something ourselves based from the IANA tz database) to really build this out functionality wise and test it, at least imo. If anyone has any thoughts, let me know 😄

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,960	95,960	0
Passed	76,534	76,534	0
Ignored	18,477	18,477	0
Failed	949	949	0
Panics	0	0	0
Conformance	79.76%	79.76%	0.00%

[codecov]

Codecov Report

Attention: 46 lines in your changes are missing coverage. Please review.

Comparison is base (a20a61a) 47.42% compared to head (c3caed9) 47.38%.

Files	Patch %	Lines
...e/engine/src/builtins/temporal/time_zone/custom.rs	0.00%	25 Missing ⚠️
...ngine/src/builtins/temporal/zoned_date_time/mod.rs	0.00%	7 Missing ⚠️
core/engine/src/builtins/temporal/time_zone/mod.rs	0.00%	6 Missing ⚠️
core/temporal/src/components/tz.rs	16.66%	5 Missing ⚠️
core/temporal/src/components/zoneddatetime.rs	33.33%	2 Missing ⚠️
core/temporal/src/components/duration.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3543      +/-   ##
==========================================
- Coverage   47.42%   47.38%   -0.04%     
==========================================
  Files         470      471       +1     
  Lines       45690    45727      +37     
==========================================
  Hits        21667    21667              
- Misses      24023    24060      +37     

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[HalidOdat]

Looks good to me! :)

[jedel1043]

Good progress! I have a suggestion for the next ergonomics change, but this can be merged as is.

[jedel1043]

Thought: We should probably add an associated error type type Error: From<TemporalError> so that we can preserve the full engine error. Would also have to be added to CalendarProtocol.

[nekevss]

That makes sense. As the change can be done on both traits. I'll update that on another PR for both traits.