perf(codecs): avoid String allocation in proc macro type checking #19354
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While looking at the derive macro code, I noticed we're converting syn::Ident to String just to compare it with string literals in should_use_alt_impl(). This creates unnecessary heap allocations during macro expansion.
Since syn::Ident already implements PartialEq<&str>, we can compare directly without the .to_string().as_str() chain. This matches the pattern already used on line 155 in the same file for the "maybe_zero" check.
The change is semantically identical but skips the temporary String allocation on every type check, which should help compile times for projects with lots of Compact derives.