feat: Reimplement support for true ESM mode

[Chooks22]

For the sake of the project's simplicity during the v2 rewrite, support for ES Modules have been temporarily dropped.

Major issues in supporting ESM is the lack of access to module cache (as opposed to CJS require.cache), so custom URL hashing, dependency chain tracking, and cache invalidation will all have to be developed (which is possible as seen in v1, but is extremely messy and still have disparities between the two modes).

In future versions, module loading could possibly be handled via messages in a client-server architecture, possibly unifying the handling for both CJS and ES modules and resulting in a clearer API.

Relevant links:

• How to invalidate ES module cache nodejs/help#1399
• Require cache equivalent in es modules nodejs/help#2806

[Chooks22]

Update on this:

vm.Module from node:vm module looks promising. vm.SourceTextModule accepts a string as its first param as the code for the module, which is easily accessible for us since we compile the code using swc.

Issue is, it doesn't seem like the memory is freed once the reference to the module is gone. Even just a simple test of the ff. increases the heap size.

import { SourceTextModule } from 'node:vm'

for (let i = 0; i < 10_000; i++) {
  new SourceTextModule('')
}

console.log(process.memoryUsage().heapUsed)