perf(ci): speed up webapp test execution (#4709)

## Summary

Speeds up webapp test jobs by balancing measured work across runners,
reducing repeated container setup, and ensuring test workers release
shutdown resources promptly. Unit tests run across 24 duration-aware
shards, while E2E tests run across two balanced shards.

## Design

`RunEngine` shutdown now closes processing resources before support
resources, continues cleanup if one close fails, and reuses one shutdown
promise for concurrent callers. Redis workers clear completed shutdown
deadlines so finished tests no longer wait on idle timers.

Container-heavy suites are split only where it improves parallelism, and
repeated replication and engine fixtures are consolidated where one
end-to-end case provides coverage. Timing weights are refreshed for all
affected files.

Dependency installation overlaps container pulls, and both workflows use
WarpBuild's Node setup action.