jsr support

[silverwind]

https://jsr.io/docs/npm-compatibility

Likely need to not ask the npm API, but the jsr API for packages on the @jsr scope.

[silverwind]

There are two different formats in package.json:

"@std/semver": "npm:@jsr/std__semver@1.0.5"
"@std/semver": "jsr:1.0.5"

Fetch metadata from https://jsr.io/@std/semver/meta.json