Doesn't handle package.json `imports` field

Nobody has claimed this yet.

the [`chalk`](https://www.npmjs.com/package/chalk) uses `imports` in the package.json. these start with a `#`. I'm not sure of the full semantics of how this "should" work. It might be as simple as switching [this](https://github.com/lukeed/tsm/blob/master/src/loader.ts#L87):

```diff
- if (/^\w+\:?/.test(ident)) return fallback(ident, context, fallback);
+ if (/^(\w+\:?|#)/.test(ident)) return fallback(ident, context, fallback);
```

but that might be too naive to work in every case.

It seems to be because the [`check`](https://github.com/lukeed/tsm/blob/master/src/loader.ts#L68-L71) function calls `fileURLToPath` from `url`, which strips the `#` and following text, meaning that the `check` function ends up just checking if the `parentURL` exists.

I think the _full_ solution to this would be to, if there's a `#` at the start of the import, call `fallback` and then process the result of `fallback`, as it might resolve to a typescript file. It _might_ be enough to just ignore any `#` files and assume that the package exposing them is not using typescript?

## Repro Steps

- `mkdir imports-report && cd imports-repro`
- `npm init -y`
- `npm add chalk tsm`
- `echo "import chalk from 'chalk';" > index.mjs`
- `node --loader tsm index.mjs`

you'll see

```
file:////imports-repro/node_modules/chalk/source/index.js#supports-color.mts:7
const { stdout: stdoutColor, stderr: stderrColor } = supportsColor;
^

TypeError: Cannot destructure property 'stdout' of 'supportsColor' as it is undefined.
at file:////imports-repro/node_modules/chalk/source/index.js#supports-color.mts:7:17
at ModuleJob.run (node:internal/modules/esm/module_job:193:25)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async Promise.all (index 0)
at async ESMLoader.import (node:internal/modules/esm/loader:527:24)
at async loadESM (node:internal/process/esm_loader:91:5)
at async handleMainPromise (node:internal/modules/run_main:65:12)
```

Start with src/loader.ts around the check function at lines 68-71 and the fallback condition near line 87. Reproduce the issue with chalk's package.json imports using the listed npm and node --loader tsm commands, then verify that # imports resolve correctly without breaking TypeScript file loading.

Written by the indexing model from the issue text.