Add caching for job list and count endpoints

[Dagonite]

Closes None (continuation of caching logic).

Description

Introduces caching for job listing and counting endpoints in the fia_api service to improve performance and reduce database load. It adds cache key generation, cache get/set logic, and environment-configurable TTLs. Added end-to-end tests to verify cache behaviour.

[codecov]

Codecov Report

❌ Patch coverage is 98.11321% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.31%. Comparing base (d15484e) to head (f2ad682).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
fia_api/routers/jobs.py	98.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #599      +/-   ##
==========================================
+ Coverage   96.28%   96.31%   +0.03%     
==========================================
  Files          48       48              
  Lines        1882     1928      +46     
==========================================
+ Hits         1812     1857      +45     
- Misses         70       71       +1     

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