fix: exclude tests from published package

[kyletsang]

Current versions of v11 are including the tests in the published package.

This PR fixes that by preventing transpilation of the test folder in the root tsconfig and uses a test-specific tsconfig which does transpile test files. The tsconfig.test.json only targets esm since the original test command uses that folder only. Declarations are not emitted because they are not used.

[broofa]

Hey, thanks for catching this. I agree removing the test files probably makes sense. (That said I vaguely recall a conversation with someone a few years back making the case for including them...? But I don't recall when / where and I can't make a good case for keeping them.)

Instead of having a separate build pipeline for the test files - which has a whiff of code smell to it - let's add an .npmignore file with the necessary incantation(s) for excluding the test dir(s).