Repo restructuring to remove circular dependencies

Related issues

• https://github.com/colinhacks/zod/issues/175#issuecomment-724316421
• https://github.com/colinhacks/zod/pull/226

RFC

• bases shouldn’t import other modules
  • for example, src/types/base.ts should be reconsidered
• api reused in other modules should be modularized, for example:
  • src/parser.ts should be split into two files
    • src/parser/index.ts & src/parser/types.ts so the circular dependency between ZodError & parser is removed
      • and a similar approach could be done on other instances of circular dependency

[colinhacks]

@o-alexandrov zod@3.0.0-alpha.7 now contains no circular dependencies.

[o-alexandrov]

@colinhacks I have tried and resolved most of them before locally, but then I read the recommendation to follow the Medium article and decided to demonstrate first that article doesn’t resolve the issue. I plan to clean up the PR on circular dependencies later this week, since:

• it seems you would approve the changes, if they wouldn’t hurt the readability (modularity) in the project