Remove custom test profile settings

[tanglearncode]

Summary

• Remove the custom test profile from the workspace manifest.
• Remove the profile setup from the README.
• Keep CI's existing incremental-cache setting unchanged.

Validation

Passed locally on Windows x64 with Cargo's default test profile:

• cargo fmt --all --check
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo test --workspace --locked -- --test-threads=1
• cargo test --test parallel --locked -- --test-threads=8

Local Docker was unavailable. Coverage was not run locally because disk space was low. Existing PR CI will validate coverage and the supported platforms.