Make watchers clearable via $watch

[Gumball12]

Related to #5

Add functionality to clear watchers via the $watch method.

• src/index.ts
  • Add a clear method to the $watch property to remove watchers from the store.
  • Implement the clearWatcher function to handle the removal of watchers.
• tests/index.test.ts
  • Add tests to verify that watchers can be cleared via the $watch method.
  • Add tests to ensure that cleared watchers do not trigger after being cleared.
• README.md
  • Update documentation to include instructions on how to clear watchers via the $watch method.

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