docs: update AGENTS local testing workflows

[shaypal5]

Summary

• document additional local-testing make targets already present in Makefile
• document parallel test options supported by scripts/test-local.sh
• add CACHIER_TEST_CORES environment-variable workflow example

Why

Keep AGENTS.md aligned with actual repo workflows/commands so automation and contributors use the same entry points.

Changes

• add make test-mongo-inmemory
• add make test-mongo-also-local
• add make services-logs
• add -p/--parallel and -w/--workers options
• add CACHIER_TEST_CORES="mongo redis" ./scripts/test-local.sh example

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (98f137b) to head (930d569).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #365   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines         1701      1701           
  Branches       213       213           
=========================================
  Hits          1701      1701           

Flag	Coverage Δ
local	58.55% <ø> (ø)
mongodb	40.91% <ø> (ø)
postgres	43.85% <ø> (ø)
redis	47.14% <ø> (ø)
s3	42.85% <ø> (ø)

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[Copilot]

Pull request overview

Updates contributor/agent documentation in AGENTS.md to better reflect existing local-testing workflows (Make targets and scripts/test-local.sh options) used across Cachier’s multi-backend test matrix.

Changes:

• Document additional make targets (test-mongo-inmemory, test-mongo-also-local, services-logs).
• Document scripts/test-local.sh parallel options (-p/--parallel, -w/--workers) and CACHIER_TEST_CORES env var usage.

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