chore(server): Replace mypy with ty

[pedro-avalos]

Description

• This PR replaces mypy with ty for type-checking
• ty outperforms mypy in speed; it also is part of the Astral toolset (of which we are using more in our org).

$ time mypy src tests
Success: no issues found in 31 source files

real    0m1.038s
user    0m0.875s
sys     0m0.162s

$ time ty check src tests
All checks passed!

real    0m0.148s
user    0m0.457s
sys     0m0.147s

(In the GitHub CI, it seems to be a difference between about 7 seconds to under 0.25 seconds)

Related Issue(s)

Untracked

Testing

• Unit tests

• Manual testing steps:

  1. uv sync
  2. uvx tox run -e lint

Checklist

• I have followed the contribution guidelines.
• I have signed the Canonical CLA.
• I have added necessary tests.
• I have added or updated any relevant documentation (if needed).
• I have tested the changes.

Additional Notes

I added a # ty: ignore[invalid-argument-type] comment on main.py because of an existing bug in ty that is not supporting ParamSpec at the moment. A follow-up PR should remove this once a fix is in place in ty.

This PR only replaces mypy in the Server project, not the Charm, for a couple reasons:

1. We are not using mypy in the Charm tests
2. When I tried to use ty (or mypy) on the Charm, I ran into a lot of errors because of the way ops packages ops.testing (ops[testing] is basically installing ops-scenario and hacking it into an ops.testing module)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.27%. Comparing base (7d67c39) to head (f3f43e0).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #504   +/-   ##
=======================================
  Coverage   89.27%   89.27%           
=======================================
  Files          28       28           
  Lines        1417     1417           
  Branches        4        4           
=======================================
  Hits         1265     1265           
  Misses        151      151           
  Partials        1        1           

Flag	Coverage Δ		*Carryforward flag
charm	100.00% <ø> (ø)		Carriedforward from d74abcb
client	80.24% <ø> (ø)		Carriedforward from d74abcb
server	97.03% <ø> (ø)		Carriedforward from d74abcb

*This pull request uses carry forward flags. Click here to find out more.

Components	Coverage Δ
Server	96.85% <ø> (ø)
Charm	97.10% <ø> (ø)
Client	80.24% <ø> (ø)

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[rene-oromtz]

Looks really nice! Super simple to migrate from mypy to ty and really fast!