test: remove environment-sensitive assertions

[fieldsofland]

Summary

• verify selected trunk colors in both ordinary and NO_COLOR environments
• assert bounded upstream work directly instead of using a scheduler-sensitive wall-clock threshold
• record the CI portability lesson in project memory and changelog

Verification

• cargo fmt --all -- --check
• cargo clippy --locked --offline --all-targets --all-features -- -D warnings
• env -u NO_COLOR cargo test --locked --offline --all-targets --all-features
• git diff --check