fix: strip parent dangling conflict commas

[pupuking723]

Fixes #115.

When a conflict block covers the final property of an object, the synthesized parent JSON can keep the separator comma from the previous top-level line:

{
  "foo": "foo",
}

That parent is only an intermediate baseline used for diff resolution, but parsing it currently throws before the selected side can be applied.

This strips dangling commas from the synthesized parent fragment before parsing it. The selected ours and theirs fragments are still parsed normally, so invalid user-provided conflict sides continue to fail.

Verification:

• npx tap --no-coverage test/basic.js
• npm run eslint -- lib/index.js test/basic.js
• git diff --check
• npm test passes tests, coverage, and eslint locally, then fails only in template-oss-check because the generated repository template wants unrelated .github branch/template updates. I did not include those unrelated tooling changes in this bugfix PR.