Enforce type-only imports via linter

## Motivation

https://app.graphite.com/github/pr/anza-xyz/kit/1035/Add-a-function-to-flatten-transaction-plan-results#comment-PRRC_kwDONc0xOc6YXyOR

## Details

Add a linter (I guess this means this really needs to be a pull request for https://github.com/anza-xyz/eslint-config-solana/) that enforces `import type { Foo } from 'foo'` when `Foo` is only used in a type position. Make sure that it works with the import sorter, and has an autofix.