port the following functions
fs.createReadStream(file): ReadableStream should add to #sitegen/fsfs.createWriteStream(file): ReadableStream should add to #sitegen/fscrypto.createHash(algo, WritableStream): Promise<string>zlib.createGzip() -> CompressionStreamzlib.createZstdCompress(): TransformStreamstream.promises.pipeline probably just use the built-in APIchild_process.spawn should add to #sitegen/subprocessreadline.createInterface(): TransformStream can derive from https://jsr.io/@std/streams/1.0.12/text_line_stream.tsthe node.js ones will probably have to be homegrown. either as wrappers around the node.js apis or whatever. it might be cute to see if other runtimes can be supported.
this can be done with more "overlay" modules like #sitegen/fs