can: refactor

This commit includes a lot of damages:

- change to a more structural pkg hierarchy: config, core, types
- refactor some modules to use a more OOP paradigm
- further integrate implicit cfg to modules
- add imm width to config
- change all modules to accept UInt, which makes all data paths in
  core UInt(512.W)
- temporary remove all test cases because of the changes above;
  they need to be rewritten
- maybe more