(test): add code coverage configuration

- gitignore coverage/ directory
- ignore asyncLocalStorage for now
  - internally we only use getItem and setItem -- the other methods
    are defined for strictly for type purposes
    - maybe keep the file in coverage but ignore the unused methods?

- (deps): update tsdx to support custom jest configs

Author: agilgur5

.gitignore

@@ -4,6 +4,7 @@ dist/
 .rts2_cache_cjs
 .rts2_cache_esm
 .rts2_cache_umd
+coverage/
 
 ### Node ###
 

jest.config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  coveragePathIgnorePatterns: [
+    '/node_modules/', // default
+    '<rootDir>/src/asyncLocalStorage.ts' // ignore for now
+  ]
+}