refactor: get rid of ReadonlyDeep type

[Lodin]

Before, all OpenAPIV3 types were wrapped in ReadonlyDeep wrapper to make them read-only. However, now, when we have TransferTypesPlugin, it looks overburdened and unnecessary. So I decided that it'd be better to just remove this type leaving raw OpenAPIV3 types. It also unwrapped several errors, so this PR contains fixes for them as well.

PR Summary

Dependency Updates:

• Updated @vaadin/react-components from version 24.7.0-alpha7 to 24.7.0-alpha8 in package.json and packages/ts/react-crud/package.json (🤖).

Type Definition Changes:

• Removed ReadonlyDeep type from various type definitions in multiple files, including Generator.ts, ReferenceResolver.ts, Schema.ts, EndpointMethodOperationProcessor.ts, EndpointMethodRequestBodyProcessor.ts, EndpointMethodResponseProcessor.ts, EndpointProcessor.ts, index.ts in generator-plugin-backbone, and index.ts in generator-plugin-model.

Code Improvements:

• Added a check to ensure all items in the oneOf array are ReferenceSchema in SubTypesPlugin.
• Updated the constructor of SubTypesProcessor to use readonly for the oneOf parameter.

These changes collectively simplify type definitions and improve the robustness of the code.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 86.91%. Comparing base (e238c32) to head (4646dab).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/ts/generator-core/src/Generator.ts	0.00%	1 Missing ⚠️
...ackages/ts/generator-core/src/ReferenceResolver.ts	0.00%	1 Missing ⚠️
packages/ts/generator-core/src/Schema.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3201      +/-   ##
==========================================
- Coverage   86.91%   86.91%   -0.01%     
==========================================
  Files         118      118              
  Lines        8194     8191       -3     
  Branches     1256     1256              
==========================================
- Hits         7122     7119       -3     
  Misses       1058     1058              
  Partials       14       14              

Flag	Coverage Δ
unittests	86.91% <75.00%> (-0.01%)	⬇️

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

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

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud

[taefi]

LGTM.