Fix manual json return

[Manar-Elhabbal7]

Description

This PR improves how the CreateTestResult() request payload is built by replacing manual JSON string concatenation with a structured approach using Go structs and json.Marshal().

Previously, building the JSON manually could lead to issues when values contained special characters like quotes or backslashes. This refactor makes the request generation safer and more reliable.

What changed

• Introduced a testRequest struct to represent the API payload.
• Replaced manual string building with json.Marshal().
• Improved handling of complex fields using json.RawMessage.
• Fixed a typo in ensureValidOAuth2Context.
• Improved OAuth2 context parsing and validation.

Impact

• Safer JSON generation
• Better code readability and maintainability
• Fewer potential runtime bugs from malformed payloads

before solving it

after solving it

Related issue(s) : #377