gh-134717: Allow overriding serialization of NaN and Infinity in json.encoder

[krzyszti]

This change modifies the json.encoder module to permit customization of how special floating-point values (NaN, Infinity, -Infinity) are serialized. By introducing a floatstr function, developers can now define alternative representations for these values, such as null, 0, or custom strings, enhancing flexibility in JSON output.

• Issue: Allow customization of NaN and Infinity serialization in json module #134717

[python-cla-bot]

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[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[sharktide]

@krzyszti
The news entry here is in the wrong place and format. Please move it to /next/Library/ and use blurb or blurb it to create the entry. The content {of the news entry} looks fine though

[sharktide]

self isn't defined here either

[nineteendo]

Also keep in mind that the C implementation will still be called if you override floatstr.