Add per-request header override loop to WriteExecute and remove stray loop

[coderabbitai]

Description

Per-request header overrides are not being applied in the WriteExecute method in api_open_fga.go. Additionally, there is a stray header override loop outside of any Execute function that should be removed.

Details

• Missing override in WriteExecute: Around line 4253, the WriteExecute function does not include the per-request header override loop that applies r.options.Headers to localVarHeaderParams.
• Stray loop: Around line 4298, there is a header override loop outside of any Execute function that should be removed to avoid potential double application.

Expected Behavior

All 17 Execute methods should apply per-request header overrides exactly once by including this loop before calling prepareRequest:

// if any override headers were in the options, set them now
for header, val := range r.options.Headers {
    localVarHeaderParams[header] = val
}

References

• PR: feat: support per-request headers options #233
• Comment: feat: support per-request headers options #233 (comment)
• Requester: @rhamzeh

Acceptance Criteria

• Add the per-request header override loop to WriteExecute method
• Remove the stray header override loop at line ~4298
• Verify all 17 Execute methods have exactly one header override application
• Add test coverage to verify WriteExecute applies custom headers correctly