fix: Represent appended AnyOf types as schema objects

[edgarrmondragon]

Summary by Sourcery

Ensure nullable composite properties produce valid JSON Schema definitions.

Bug Fixes:

• Represent appended types in anyOf and oneOf schemas as valid JSON Schema subschema objects.

Tests:

• Add regression coverage validating optional composite types against the JSON Schema meta-schema.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Fix append_type so types added to existing anyOf schemas are represented as full JSON Schema objects, with corresponding test coverage updated for null appends.

File-Level Changes

Change	Details	Files
Normalize appended AnyOf entries to complete JSON Schema type objects.	Wrap the new type in {"type": new_type} before comparing or appending. Preserve duplicate detection and scalar-to-list conversion while using full schema objects.	singer_sdk/helpers/_typing.py
Update typing behavior coverage to expect schema objects in anyOf.	Change the anyOf conformance expectation for appended null from a bare string to {"type": "null"}.	tests/core/test_typing.py

---

Tips and commands

Interacting with Sourcery

• Trigger a new review: Comment @sourcery-ai review on the pull request.
• Continue discussions: Reply directly to Sourcery's review comments.
• Generate a GitHub issue from a review comment: Ask Sourcery to create an
  issue from a review comment by replying to it. You can also reply to a
  review comment with @sourcery-ai issue to create an issue from it.
• Generate a pull request title: Write @sourcery-ai anywhere in the pull
  request title to generate a title at any time. You can also comment
  @sourcery-ai title on the pull request to (re-)generate the title at any time.
• Generate a pull request summary: Write @sourcery-ai summary anywhere in
  the pull request body to generate a PR summary at any time exactly where you
  want it. You can also comment @sourcery-ai summary on the pull request to
  (re-)generate the summary at any time.
• Generate reviewer's guide: Comment @sourcery-ai guide on the pull
  request to (re-)generate the reviewer's guide at any time.
• Resolve all Sourcery comments: Comment @sourcery-ai resolve on the
  pull request to resolve all Sourcery comments. Useful if you've already
  addressed all the comments and don't want to see them anymore.
• Dismiss all Sourcery reviews: Comment @sourcery-ai dismiss on the pull
  request to dismiss all existing Sourcery reviews. Especially useful if you
  want to start fresh with a new review - don't forget to comment
  @sourcery-ai review to trigger a new review!

Customizing Your Experience

Access your dashboard to:

• Enable or disable review features such as the Sourcery-generated pull request
  summary, the reviewer's guide, and others.
• Change the review language.
• Add, remove or edit custom review instructions.
• Adjust other review settings.

Getting Help

• Contact our support team for questions or feedback.
• Visit our documentation for detailed guides and information.
• Keep in touch with the Sourcery team by following us on X/Twitter, LinkedIn or GitHub.

[edgarrmondragon]

@sourcery-ai title

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.38%. Comparing base (674db6f) to head (ece5e1c).

Files with missing lines	Patch %	Lines
singer_sdk/helpers/_typing.py	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3770   +/-   ##
=======================================
  Coverage   94.37%   94.38%           
=======================================
  Files          74       74           
  Lines        6298     6300    +2     
  Branches      771      772    +1     
=======================================
+ Hits         5944     5946    +2     
  Misses        265      265           
  Partials       89       89           

Flag	Coverage Δ
core	83.09% <50.00%> (+<0.01%)	⬆️
end-to-end	75.68% <16.66%> (-0.03%)	⬇️
optional-components	44.96% <16.66%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[codspeed]

Merging this PR will not alter performance

✅ 14 untouched benchmarks

---

_{Comparing fix/anyof-null (ece5e1c) with main (674db6f)}