perf(span): align Span same as usize

[overlookmotel]

Span consists of 2 x u32 (8 bytes total). Align Span on 8 bytes on 64-bit platforms. This means that, on 64-bit platforms, Span can be treated as equivalent to a u64 and stored in a single register (instead of requiring 2).

A side-effect is that all AST structs also become aligned on 8. This will be a useful property later on as we can remove alignment calculations from Allocator::alloc (since everything now has same alignment).

BooleanLiteral (and BoundaryAssertion, CharacterClassEscape and IndexedReference from oxc_regular_expression crate) increase from 12 bytes to 16 bytes due to the higher alignment. But this makes no practical difference as they'd almost always end up with padding around them in arena anyway, as they'll be surrounded by 8-aligned types.

[overlookmotel]

• perf(span): compare Spans as single u64s #8300
• perf(span): hash Span as a single u64 #8299
• refactor(span): all methods take owned Span #8297
• perf(span): align Span same as usize #8298 👈 (View in Graphite)
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #8298 will improve performances by 4.92%

_{Comparing 01-03-perf_span_align_span_same_as_usize_ (1b5a978) with main (d8b27af)}

Summary

⚡ 1 improvements
✅ 28 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	01-03-perf_span_align_span_same_as_usize_	Change
⚡	isolated-declarations[vue-id.ts]	725.1 ms	691.1 ms	+4.92%