Add env-based time limits

[aobolensk]

• read optional env vars PPC_TASK_MAX_TIME and PPC_PERF_MAX_TIME
• use those env vars when checking execution time
• document new environment variables
• add regression tests for the env vars

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.72%. Comparing base (8b3e8fb) to head (e4fde35).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #525      +/-   ##
==========================================
+ Coverage   94.57%   94.72%   +0.15%     
==========================================
  Files          11       11              
  Lines         350      360      +10     
  Branches      117      122       +5     
==========================================
+ Hits          331      341      +10     
  Misses          5        5              
  Partials       14       14              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

Coverage report is available for download
here

[github-actions]

Coverage report is available for download
here