fix: stable option diff to prevent spurious remounts & stale config

[ApexYash11]

Summary

Fixes #66 — the wrapper diffed options prop changes by stringifying the
option objects with JSON.stringify and comparing the strings
(remountKey / updatableKey in src/ImageEditor.tsx). That approach had
three failure modes:

1. Key-order sensitivity — semantically identical options differing only
   in property declaration order produced different keys → a spurious
   remount (destroying unsaved edits — the README explicitly warns
   remount-tier options discard edits, so this is data loss) or a spurious
   updateOptions.
2. Dropped undefined / functions — JSON.stringify silently omits them,
   so real changes inside options (e.g. a user field) were invisible to the
   diff → stale editor configuration without warning.
3. Throws on circular references — a circular reference inside options
   crashed during render.

Change

Adds src/optionsDiff.ts, a stable canonical serializer (stableKey) that:

• sorts object keys, so equal structures always serialize to equal strings in
  either key order (fixes chore(deps): Bump actions/checkout from 4 to 7 #1);
• treats undefined and functions as first-class values — functions are keyed
  by stable reference id, so a real change is never invisible (fixes chore(deps): Bump actions/setup-node from 4 to 6 #2);
• emits a marker for circular references instead of recursing forever, so a
  circular options object can no longer crash render (fixes chore(deps): Bump codecov/codecov-action from 5 to 7 #3).

ImageEditor.tsx now uses stableKey for remountKey, updatableKey, and the
mount-time appliedUpdatableRef recording, replacing all three JSON.stringify
sites (consistently, so initial apply / updateOptions guards stay in sync).

Tests

• test/optionsDiff.test.ts — new unit tests for key-order insensitivity,
  dropped-field visibility, function-by-reference stability, circular-reference
  safety, and every primitive branch.
• test/index.test.tsx — new component tests: no remount/updateOptions on
  key-order-only change, a remount is correctly detected when a
  previously-undefined value becomes defined, and rendering with a circular
  options object mounts exactly once without crashing.

Verification

• npm run typecheck — passes
• npm run test:coverage — 55/55 tests pass, 100% statements / branches /
  functions / lines across src/**
• Prettier clean on all changed files (matches repo line-ending policy)

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