refactor(temporal): extract this-type-check boilerplate into a macro

[Nakshatra480]

Summary

This PR removes the repetitive this-type-check boilerplate present in almost every Temporal prototype method.

Previously, each method manually called this.as_object(), downcasted with .as_ref().and_then(JsObject::downcast_ref::<Self>), and threw a TypeError on failure - 5 lines repeated 158 times across 8 files.

I've extracted this into a single this_temporal_object! macro in temporal/mod.rs. A helper function isn't viable here because this.as_object() returns an owned JsObject that the resulting Ref<T> borrows from - the owner must live in the caller's scope. The macro solves this by emitting the let bindings directly there.

Changes

• Replaced 158 occurrences of the type-check boilerplate across 8 Temporal modules with the new macro
• Unified all TypeError messages to "the this object must be a {Type} object." - a few types like Duration previously used inconsistent phrasing
• Net delta: +183 / -1,106 lines

N downcast_ref::<Self> calls in static ::from() methods are deliberately left untouched - those check item, not this.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,732	50,732	0
Ignored	1,426	1,426	0
Failed	805	805	0
Panics	0	0	0
Conformance	95.79%	95.79%	0.00%

Tested main commit: 2437b6704c4315f6ec8f0766bf229fba23e0e61e
Tested PR commit: 2fdc570ea4f0449516cd7d3c19712c52d772bb9f
Compare commits: 2437b67...2fdc570

[codecov]

Codecov Report

❌ Patch coverage is 3.03030% with 160 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.39%. Comparing base (6ddc2b4) to head (56ac6f3).
⚠️ Report is 918 commits behind head on main.

Files with missing lines	Patch %	Lines
.../engine/src/builtins/temporal/zoneddatetime/mod.rs	0.00%	47 Missing ⚠️
...ngine/src/builtins/temporal/plain_date_time/mod.rs	2.70%	36 Missing ⚠️
...ore/engine/src/builtins/temporal/plain_date/mod.rs	0.00%	15 Missing ⚠️
...ore/engine/src/builtins/temporal/plain_time/mod.rs	6.25%	15 Missing ⚠️
...gine/src/builtins/temporal/plain_year_month/mod.rs	0.00%	15 Missing ⚠️
core/engine/src/builtins/temporal/instant/mod.rs	0.00%	12 Missing ⚠️
core/engine/src/builtins/temporal/duration/mod.rs	23.07%	10 Missing ⚠️
...ngine/src/builtins/temporal/plain_month_day/mod.rs	0.00%	8 Missing ⚠️
core/engine/src/builtins/temporal/mod.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5233       +/-   ##
===========================================
+ Coverage   47.24%   60.39%   +13.15%     
===========================================
  Files         476      589      +113     
  Lines       46892    62753    +15861     
===========================================
+ Hits        22154    37902    +15748     
- Misses      24738    24851      +113     

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[nekevss]

I do sort of like the change for how succinct it is, and it's potential for making the code more readable.

One question: why change just the temporal objects and not the built-ins in general? Had you looked at other built-ins?