Add `crypto.key` module

Nobody has claimed this yet.

The current `worktop/crypto` module has `keyload` and `keygen` methods, but they're really not all that helpful. I end up dropping into `crypto.subtle.importKey` (and others) directly quite often, which is a good signal that something should be done here.

Additionally, the native TS definitions for `importKey` et all are pretty useless... With custom methods, I should be able to accurately offer _strict overloads_ so that you can only have/define valid combinations. For example, for [`importKey`](https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/importKey#supported_formats) has its own restrictions and `generateKey` has different input requirements based on format. Both of these can offer much better types - and possibly a tiny abstraction.

Start with the worktop/crypto module and compare its keyload and keygen helpers with crypto.subtle.importKey and generateKey, using the linked MDN supported-format restrictions as the reference. Define the intended strict overload coverage and abstraction boundary; done means the requested key operations expose valid combinations through TypeScript types.

Written by the indexing model from the issue text.