fix(visitor): dispatch on DataType from another copy

[kentkwu]

What's Changed

getVisitFn used instanceof DataType, which fails for a type created by another copy of the library, such as the CommonJS and ES module builds loaded side by side. The visitor fell through to Type.NONE, so the IPC writer silently wrote a stream with no types and empty bodies.

Applies a fix to use DataType.isDataType() introduced in #377, which works across copies, and adds a test that writes tables through a second copy of the library.

Closes #496

[ianmcook]

Looks good to me!

A couple of nits found with help from Claude Opus 5.5:

• The as any casts in the test aren't needed. Other has type typeof Arrow, and tsc passes with the casts removed.
• This is the first test in the repo to import @jest/globals. That package isn't a declared devDependency and only resolves because jest depends on it.