Proposed changes

Fixes: #5532
This PR adds focused fuzz coverage for MarshalGQLData in chaoscenter/subscriber/pkg/graphql.

The fuzz test validates that JSON-marshalable subscriber payloads are processed without unexpected errors and that the returned GraphQL payload is safely quoted, contains no raw line terminators, and can be unquoted successfully. It also adds negative coverage for unsupported marshal inputs such as function values, NaN, and Inf.

Types of changes

• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices applies)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the commit for DCO to be passed.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

Dependency

None.

Special notes for your reviewer

Verified locally with:

cd chaoscenter/subscriber
go test ./pkg/graphql
go test ./pkg/graphql -run=^$ -fuzz=FuzzMarshalGQLData -fuzztime=30s