fix: clone input schemas before transforming them

[pvdbosch]

Description

Transformation from OpenAPI to JSON draft4 schema modifies the input data, even though cloneSchema: true is used.
This leads to the bug described in #275 when the same schema is transformed multiple times during parsing.

This PR adds a deep clone step before the transformation, and a test case to validate the fix.

Upgrading @openapi-contrib/openapi-schema-to-json-schema might also fix this, but it's backwards-incompatible and I'm not well versed in typescript to make the necessary code changes.

Related issue(s)

Resolves #275

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
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

[github-actions]

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[pvdbosch]

I fixed a test that was failing after latest merge with master, but the test failing in the GitHub Actions build seems another one. Still a mystery to why it's failing because I can't reproduce it locally. I'm trying to investigate further.

[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

[pvdbosch]

Tests are working now on my forked github build.

There were missing await statements in another test somehow interfering, and the node.js version also needed to be updated to a newer one that supports structuredClone. I set minimum version to Node.js 18, aligned with https://github.com/asyncapi/parser-js/blob/master/package.json

Could you review these latest changes?