fix: correct various issues with cjs and esm dists

[fallenoak]

This PR cleans up various issues with cjs and esm dists:

• All src/ files are now flagged as esm via a package.json file at the root of src/ using { "type": "module" }
• Compiled cjs and esm files are now given an extension of .js, permitting the package.json type directives in the dist/cjs and dist/esm directories to declare the effective module type
• Root-level exports are individually named, fixing issues with default import handling for cjs (ie. no more require('@wowserhq/io').default;)