fix: safely alias schema properties and transform root xml to x-xml

[RohithPariki]

Description

This PR improves the schema traversal safety in iterateSchema and aliasProps within @asyncapi/openapi-schema-parser:

1. Adds safety guards for non-object, null, or boolean schema values in iterateSchema and aliasProps. Previously, properties with primitive values, boolean schemas (e.g., additionalProperties: false, boolean items), or null values could cause TypeError when attempting property lookups.
2. Supports converting xml to x-xml on top-level root schema objects in addition to nested properties.
3. Adds automated unit tests covering XML property aliasing and safe handling of boolean/primitive schema values.

Changes Made

• Added object validation guards in iterateSchema and aliasProps in src/index.ts.
• Added root xml to x-xml aliasing in iterateSchema.
• Added unit tests in test/parser.spec.ts.

Checks

• npm test passes (9/9 tests pass) with 98.27% code coverage.
• npm run lint passes with 0 warnings/errors.
• npm run build succeeds (both ESM and CJS).

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[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