chore(python): Bring Pyright's type completeness to 99.7%, enforce minimum 99% type coverage in CI

[MarcoGorelli]

Follow-up to #22962

The idea is to use pyright --verifytypes to enforce type completeness across the library

With this change, it brings type completeness to 99.7%. Without it, we get

           "message": "Type is missing type annotation and could be inferred differently by type checkers\n  Inferred type is \"DataFrame\"",

The remaining types reported as "partially unknown" are:

• jemalloc_conf
• override
• CredentialProviderAzure
• OptionType
• DataTypeMappings
• DataTypeGroup
• CredentialProviderAzure
• polars.lazyframe.opt_flags._ (?)

Unfortunately, pyright doesn't give us a way to enforce minimum type completeness microsoft/pyright#10458, they suggested to make a tool which wraps Pyright and parses the output json. That's what I've done in pyright-cov

Potential alternatives:

• just vendor the pyright_cov.py file into the Polars repo. It's very simple, only ~50 lines long, nothing fancy
• don't enforce minimum type completeness at all

---

I've been trying something similar in NumPy, and they've suggested BasedPyright - will take a look at that and then update numpy/numpy#29065 (comment)

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.32%. Comparing base (35f6e9f) to head (e9d2385).
Report is 62 commits behind head on main.

Files with missing lines	Patch %	Lines
.../polars/io/cloud/credential_provider/_providers.py	0.00%	1 Missing ⚠️
py-polars/polars/lazyframe/opt_flags.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22965      +/-   ##
==========================================
- Coverage   80.33%   80.32%   -0.02%     
==========================================
  Files        1682     1682              
  Lines      223120   223114       -6     
  Branches     2804     2803       -1     
==========================================
- Hits       179251   179223      -28     
- Misses      43201    43223      +22     
  Partials      668      668              

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