chore: upgrade to rust 1.78

[ematipico]

Summary

The compiler and clippy got better and I had to remove a bunch of unused code. However, there are some false positives (the empty_docs in biome_wasm) and things to review around the FormatInto inside the JSON formatter: weirdly, the trait isn't flagged inside other crates.

Test Plan

CI should pass

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	49701	49701	0
Passed	48721	48721	0
Failed	980	980	0
Panics	0	0	0
Coverage	98.03%	98.03%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	6322	6322	0
Passed	2036	2036	0
Failed	4286	4286	0
Panics	0	0	0
Coverage	32.20%	32.20%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	662	662	0
Passed	593	593	0
Failed	69	69	0
Panics	0	0	0
Coverage	89.58%	89.58%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	17646	17646	0
Passed	13439	13439	0
Failed	4205	4205	0
Panics	2	2	0
Coverage	76.16%	76.16%	0.00%

[arendjr]

Nice!

[codspeed-hq]

CodSpeed Performance Report

Merging #2691 will improve performances by 8.05%

_{Comparing chore/bump-rust (e2a0562) with main (1f891f5)}

Summary

⚡ 2 improvements
✅ 86 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	chore/bump-rust	Change
⚡	dojo.js[cached]	45.7 ms	42.6 ms	+7.31%
⚡	db.json[uncached]	87 ms	80.5 ms	+8.05%