Add JS packaging for verification functions

[bgins]

This is a draft PR that still needs work! It's open to initial feedback, but see the remaining tasks section to get an idea of what needs to be implemented.

Description

This PR implements the following features:

• [x] Add TypeScript bindings for checkSignature, decode, isExpired, isTooEarly, toCID, validate functions
• [x] Add ucan-wasm crate with JavaScript packaging support
• [x] Add packaging support for browser, node, deno, and workerd targets (workerd is Cloudflare workers)

Link to issue

Implements #93

Type of change

• [x] New feature (non-breaking change that adds functionality)

Test plan (required)

The test suite includes unit tests for each function. Tests read from a set of fixtures written in the style of the spec repo fixtures (https://github.com/ucan-wg/spec/tree/main/fixtures/0.8.1) but upgraded to UCAN 0.9.0. (Side note: It would be nice to eventually add these to the spec repo and pull them from there.)

The tests are run in node and headless browser environments including chromium, firefox, and webkit.

Remaining tasks

• [ ] Upgrade to UCAN 0.10.0
• [ ] Convert test fixtures to UCAN 0.10.0
• [ ] Optimize for size where possible
• [ ] Investigate DID parsing options. Bringing in key support here doubles the size of the Wasm binary:

https://github.com/ucan-wg/rs-ucan/blob/8520742bad4de0f9ba4d5f3004a7292d27cf363e/ucan-wasm/src/ucan/verify.rs#L15-L19

• [ ] Add bindings for more validation functions
• [ ] Add deno tests
• [ ] Add workerd tests (if possible)
• [ ] Add bundler tests for a couple of commonly used bundlers