[Documentation bug]: `httpOperation.get` toolkit always return new httpoperation for the same operation

### Describe the bug

in the same program, each time i called `httpOperation.get` toolkit, i'll get a new http operation type. does the cache work? digging into the [code](https://github.com/microsoft/typespec/blob/9abfb50239af90e4f4348be1e65f8e308533d19d/packages/http/src/operations.ts#L32), it seems the cache is not bind in the program, but always creating a new map.

### Reproduction

call `httpOperation.get` twice.

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.