fix(mimetype-content-wrapper): clone object per mimetype to avoid shared references

[yogeshwaran-c]

Summary

MimetypeContentWrapper#wrap builds the OpenAPI content object by mapping each media type to removeUndefinedKeys(obj) — but it reuses the same object reference for every media type and passes the caller's object directly into removeUndefinedKeys (which mutates in place).

Two consequences for responses/request bodies declared with multiple media types (e.g. @ApiProduces('application/json', 'application/xml') or multiple @ApiConsumes):

1. Aliased entries — every media-type entry in content points to the same object instance, so mutating one media type's schema later silently mutates all of them.
2. Source mutation — removeUndefinedKeys strips keys from the caller's original object rather than a copy.

Reproduction (current behavior):

const { content } = new MimetypeContentWrapper().wrap(
  ['application/json', 'application/xml'],
  { schema: { type: 'string' } }
);

content['application/json'] === content['application/xml']; // true (bug)
content['application/json'].schema.type = 'mutated';
content['application/xml'].schema.type; // 'mutated' (leaked)

The fix clones the object per media type with lodash cloneDeep (already used elsewhere in the codebase) so each entry is independent and the caller's source object is left untouched.

Test plan

Added test/services/mimetype-content-wrapper.spec.ts covering:

• wrapping under each provided mimetype
• stripping undefined keys
• distinct object/schema references between media types (fails before the fix)
• caller's source object is not mutated (fails before the fix)

npx vitest run test/services            # 71 passed (incl. new spec)
npm run lint                            # exit 0
npm run build                           # exit 0