test: Helper unit tests have hard dependency on @asyncapi/parser ('test isolation violation')

[SHUBHANSHU602]

Several helper unit test files directly instantiate real models from @asyncapi/parser, for example:

new Message(...)
new Schema(...)
new AsyncAPIDocument(...)
new TagV2(...)

Affected files:

src/helpers/__tests__/message.test.ts src/helpers/__tests__/schema.test.ts src/helpers/__tests__/sidebar.test.ts sc/helpers/__tests__/specification.test.ts
This creates a hard runtime dependency between helper unit tests and parser internals.

[AceTheCreator]

Please don't open issues that re not necessary for the sake of GSoC, please refrain from doing that.