Add Exhaustive DejaGnu directives lookup table & update rustc-1.49.0 paths

[MahadMuhammad]

• Added equivalent-dejagnu-directive.md, a mapping of Rustc compiletest test header directives to their DejaGnu equivalents

Note

It is not possible that there exists all equivalent 1-1 rustc to dejagnu directives, we are just added here for completeness

• Updated string formatting to use Rust's inline {var} syntax for improved consistency in src/errors.rs, src/header.rs, and src/transform.rs.

• Fixed lifetime annotations in function signatures in src/header.rs to ensure correct lifetimes for returned values.

• Updated the test copying path in run.sh to use rustc 1.49.0 ui tests src/test/ui instead of latest rustc directory format tests/ui

• Update README.md to include rustc-1.49.0 and gccrs repo