Resolve conflicts for RUv2 executor accounting PR

[AmoebaProtozoa]

Summary

This merges current pingcap/tidb master into meiking:fix/ruv2-executor-accounting-master to resolve the conflicts on pingcap#68578.

The manual resolution keeps the RUv2 executor/accounting logic from the original PR while preserving the RUv2 optimization work already merged on master:

• keep master's cached RUv2 executor metadata and hot L1 recorder path
• port the PR's concrete executor metric coverage into master's switch-based lookup
• keep cold RUv2 counters in ruv2MetricsExtra
• add the PR's writeKeys and writeSize counters into the optimized extra storage path

Validation

• go test -c ./pkg/executor/internal/exec -o /tmp/tidb-68578-pr-exec.test
• go test -c ./pkg/util/execdetails -o /tmp/tidb-68578-pr-execdetails.test
• go test -c ./pkg/executor -o /tmp/tidb-68578-pr-executor.test
• targeted git diff --check --cached on the manually resolved files
• checked resolved executor-type coverage against the original PR branch