refactor: split source parser into separate crate

[xxchan]

Reason: "parser" (encoding related stuff) is self-contained, and does not relate with external systems.

Benefits:

• speed up compile time and DX
• Do some refactor at the same time to make the code more organized.
• Refactor tests into UT test: better organize source test with different encodings #16931

related: #16841

[xxchan]

Similarly for sink encoder. (But maybe we can put them together, instead of two crates? Not sure 🤔 (But more crates don't hurt))