refactor: simplify redundant string conversions

[MamunC0der]

Removes unnecessary .to_string().as_str() patterns that cause redundant allocations.

• Simplified string conversions in colored_printer.rs and test_utils.rs
• No functional changes, optimization only

[reviewable-StarkWare]

This change is 

[orizi]

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[orizi]

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---

crates/cairo-lang-sierra-to-casm/src/invocations/test_utils.rs line 220 at r1 (raw file):

pub fn compile_libfunc(libfunc: &str, refs: Vec<ReferenceExpression>) -> ReducedCompiledInvocation {
    let long_id = cairo_lang_sierra::ConcreteLibfuncLongIdParser::new()
        .parse(libfunc)

run ./scripts/rust_fmt.sh or close PR.

[orizi]

@orizi reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @MamunC0der)

[orizi]

@orizi reviewed 1 of 1 files at r3.
Reviewable status: all files reviewed (commit messages unreviewed), all discussions resolved (waiting on @MamunC0der)

[orizi]

@orizi reviewed all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @MamunC0der)