Fix valueFromAST variable own-property checks

[abishekgiri]

Summary

Fixes an issue in valueFromAST where own-property checks were not properly enforced, which could lead to incorrect handling of inherited properties.

Changes

• Updated own-property checks to ensure only direct properties are considered
• Prevent unintended prototype chain access

Testing

• Verified behavior manually with edge cases
• Existing tests pass locally

[vercel]

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: abishekgiri / name: Abishek Kumar Giri (702e107)
• ✅ login: abishekgiri / name: giria660 (89efacc)

[abishekgiri]

Status update

• Fixed valueFromAST() to use own-property checks when deciding whether a variable was provided.
• Added regression coverage for omitted prototype-colliding names like toString across scalar, list, and input-object cases.
• Results: targeted mocha, eslint, and prettier checks passed for this change.
• tsc in this environment still reports existing external errors from ../node_modules/@types/react-dom, which are outside this PR.