Fix Number.prototype.toFixed()

[HalidOdat]

This Pull Request fixes/closes #2609 .

This depends on the implementation of Number.prototype.toFixed() on boa-dev/ryu-js#35.
Added the tests about the rounding (which test262 does not check) on ryu-js and here just in case :)

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,574	95,574	0
Passed	75,273	75,273	0
Ignored	19,482	19,482	0
Failed	819	819	0
Panics	0	0	0
Conformance	78.76%	78.76%	0.00%

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (c56a706) 49.56% compared to head (bc1eb23) 49.55%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2898      +/-   ##
==========================================
- Coverage   49.56%   49.55%   -0.01%     
==========================================
  Files         446      446              
  Lines       43716    43712       -4     
==========================================
- Hits        21666    21663       -3     
+ Misses      22050    22049       -1     

Files	Coverage Δ
boa_engine/src/builtins/number/mod.rs	85.87% <100.00%> (+0.12%)	⬆️

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[jedel1043]

The ryu-js PR was merged, so we can publish a new version then merge this :)

[HalidOdat]

The ryu-js v1.0.0 version has been published and this PR has been updated, so this is ready for review/merge :)

[jedel1043]

Really nice work! Hopefully with the new ryu-js CI we'll be able to integrate the remaining formatting methods a bit quicker.