Unnecessary files are included in the published packages

**Describe the bug**
Most (none?) packages don't distinguish between files that are necessary for end-projects and development-related files that happen to be inside the same folder.

**Steps to Reproduce**
For example, in the package for [`@std/msgpack`](https://jsr.io/@std/msgpack), the test spec modules, and test data files are also included.

**Expected behavior**
The packages implement filters described in https://jsr.io/docs/publishing-packages#filtering-files

**Environment**
Not applicable