Add executor-level TTL for cached results

[foreverest]

Summary

• resolves Add TTL support for cached idempotency results #19
• document executor ttl configuration in README and Cache TTL section
• ensure RedisCache honors ttlMs when provided and surfaces errors for expiration failures
• normalize executor-level ttl, apply it to cached values/errors, and validate positive values
• cover ttl behavior in cache and executor tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (937ca6b) to head (e4aa213).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #24   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          213       222    +9     
  Branches        45        46    +1     
=========================================
+ Hits           213       222    +9     

Flag	Coverage Δ
node20.x	100.00% <100.00%> (ø)
node22.x	100.00% <100.00%> (ø)
node24.x	100.00% <100.00%> (ø)

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