fix: Use jiff everywhere

[aawsome]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.3%. Comparing base (a6f4589) to head (0f5004a).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/backend/src/rest.rs	0.0%	5 Missing ⚠️
crates/core/src/repository/warm_up.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
crates/core/src/repository/warm_up.rs	11.6% <0.0%> (ø)
crates/backend/src/rest.rs	0.0% <0.0%> (ø)

... and 32 files with indirect coverage changes

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