Allow running without zino.toml

[hmpf]

Scope and purpose

Fixes #458

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is.
More information about contributing to Zino can be found in the
README.

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done

[github-actions]

Test results

666 tests   665 ✅  28s ⏱️
  1 suites    0 💤
  1 files      1 ❌

For more details on these failures, see this check.

Results for commit ddb3060.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.79%. Comparing base (e2efbcd) to head (ddb3060).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #461      +/-   ##
==========================================
+ Coverage   98.71%   98.79%   +0.08%     
==========================================
  Files          83       83              
  Lines       10092    10093       +1     
==========================================
+ Hits         9962     9971       +9     
+ Misses        130      122       -8     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[hmpf]

NTS: this is harder than I thought. Move validate_file_can_be_opened() and use it outside of the config models.

[lunkwill42]

Really, this is just a lot of faffing about. The code was already designed to run without a config file, but the main() method used an incorrect reference to the running config.

#466 is my suggestion for an alternative to this PR.

[lunkwill42]

model_validate() is a classmethod. Why did you change this?

[hmpf]

I got an error when running tests.