chore(compiler): eliminate warnings

[martian56]

Summary

• remove unused compiler imports and dead helper code
• compile compiler test modules only during test builds
• clean unused test bindings and keep the variable test self-contained
• leave the compiler crate warning-free without suppressing diagnostics

Testing

• cargo +1.96.0 check --package compiler --all-targets --locked
• cargo +1.96.0 clippy --package compiler --all-targets --no-deps --locked -- -D warnings
• cargo +1.96.0 test --package compiler --locked
• parser, validator, transpiler, and compiler CI package tests

The self-contained variable-test change also appears in #30 so this branch remains independently testable before that PR merges.

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[Prestgg1]

Thanks you for your support