feat(cache): name the changed env var in cache-miss message

[wan9chi]

Motivation

The task runner already detects which fingerprinted env vars changed between cache entries, but the inline cache-miss status collapsed that detail to envs changed. That made the live output less useful than the persisted detailed summary.

Changes

• Add EnvMismatch::name() so cache display code can reuse the detected env var name.
• Render inline env cache misses as env 'NAME' changed or envs 'A', 'B' changed.
• Update the cache-miss snapshots that exercise env additions, removals, value changes, and per-env cache keys.
• Add the changelog entry for feat(cache): name the changed env var in cache-miss message #438.

Verification

• cargo test -p vite_task_bin --test e2e_snapshots cache_miss_reasons
• cargo test -p vite_task_bin --test e2e_snapshots individual_cache_for_env
• cargo fmt
• cargo check --all-features
• cargo clippy --all-features -- -D warnings
• cargo test

[wan9chi]

• feat(cache): name the changed env var in cache-miss message #438 👈 (View in Graphite)
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.