[Perf] Use heuristics to avoid allocations in Sanitizer::str_till_eol

[ljedrz]

(transferred from ProvableHQ#6, and asking @d0cd for a review as suggested there)

The Sanitizer is used very prominently in our parsing functions, and it is also a source of many allocations, most of which are temporary and avoidable.

The potential perf improvements are quite large, and I've measured them both with a 15-minute run of a --dev node and using hyperfine on a small binary that parsed all the valid .aleo programs currently present in the snarkVM codebase.

dev node:

• all allocs are down ~15%, of which almost all are temporary
• in Program::from_str specifically, allocs are reduced by ~64%, of which temp allocs ~88%

parsing all .aleo programs using Program::from_str:

• allocs are reduced by ~41%
• growth reallocs are down ~70%
• runtime is reduced by ~31%

[ljedrz]

CI run link

[raychu86]

@ljedrz Could you fix the cargo fmt issue and rerun CI?

[ljedrz]

The fmt issue doesn't come from this PR, but seems to be caused by the new nightly compiler, meaning it would happen in all the other PRs as well. While I recommend it to be handled in its own PR, this is a new CI branch for this one.

[vicsn]

Superseded by #2563 to merge in aleonet/staging

[ljedrz]

Superseded by #2563.