feat: make dict validator strict by default

[PrettyWood]

Change Summary

Make the dict_validator strict by default.
Add a way to keep old behaviour with loose_dict_validator flag in BaseConfig

Related issue number

closes #1268
closes #1982

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #2211 (4f6ad91) into master (3496a47) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #2211   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         4121      4121           
  Branches       829       830    +1     
=========================================
  Hits          4121      4121           

Impacted Files	Coverage Δ
pydantic/dataclasses.py	100.00% <100.00%> (ø)
pydantic/error_wrappers.py	100.00% <100.00%> (ø)
pydantic/fields.py	100.00% <100.00%> (ø)
pydantic/validators.py	100.00% <100.00%> (ø)

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[samuelcolvin]

I think a feature flag for this is too confusing. We should just wait for v2, hopefully not too long now.

I'm really hoping to make some time to do the refactoring required for v2 in january.

[PrettyWood]

Glad to read that! Don't hesitate if we can help :)
If this is deferred I would like to still add the documentation to explain the "how to change globally pydantic behaviour" probably in #2193 . WDYT?

[samuelcolvin]

I'm always happy to accept a PR to improve documentation.

I'm just hesitant to make fundamental behaviour changes (even behind feature flags) within v1, especially since I think we're approaching the end of the v1 lifespan.

[HansBrende]

@PrettyWood @samuelcolvin here are some slightly less intrusive tweaks that would fix the bugs while retaining the existing behavior of being able to parse a dict from a list of tuples... would it make sense to add something like one of these before v2?

#2513 (comment)
#2513 (comment)

I would be happy to submit a PR (if desired), or not, if I hear either an affirmative or a negative response, respectively...

[samuelcolvin]

fixed in v2, omit for v1.10