[codex] Fix no-variable operations with provided variables

[zth]

Summary

Adds a regression test for a mutation that has no user-supplied variables but spreads a fragment with a Relay provided variable, then fixes the crash by normalizing converted operation variables before they are handed to Relay.

Root Cause

For operations whose variables type is unit, ReScript emits JavaScript undefined. Relay expects operation variables to be an object and reads from variables[def.name] before applying params.providedVariables, so a no-variable mutation with only provided variables crashes while creating the operation descriptor.

Changes

• Added a mutation repro that spreads a provided-variable fragment.
• Normalized converted operation variables through internal_cleanObjectFromUndefinedRaw before Relay calls.
• Applied the normalization consistently across mutation, query, subscription, preload/load, retain, local payload, and refetch paths.

Validation

• yarn build
• yarn test --runTestsByPath __tests__/Test_mutation-tests.js --runInBand
• yarn test:ci

[zth]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

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