refactor: pypi mapping module so that its a bit more logically named

[tdejager]

Description

This does a large-scale refactor of the pypi mapping module, I found it was a bit hard to reason about and the types were a bit scattered. This centralizes the different mapping resolvers and does a rename of a lot of of different structs and methods. The functionality has remained identical.

Biggest changes:

• Reorganized the crate around explicit purl derivation concepts:
  • PurlDerivationClient
  • PurlDerivationMode
  • PurlDerivationSource
  • ProjectDefinedMappingLocation
• Centralized the concrete resolver implementations under resolvers/:
  • project_defined_mapping.rs
  • prefix_hash_resolver.rs
  • prefix_compressed_resolver.rs
  • conda_forge_verbatim.rs
• Renamed ambiguous mapping/client types:
  • MappingClient → PurlDerivationClient
  • MappingSource → PurlDerivationMode
  • MappingLocation → ProjectDefinedMappingLocation
  • CustomMapping → ProjectDefinedMapping
  • MappingLocation::Memory → ProjectDefinedMappingLocation::InMemory
• Replaced the generic DerivePurls trait with explicit resolver methods.
• Introduced DerivationOutcome to make the distinction between “not applicable”, “known no purls”, and “derived purls” explicit.
• Moved shared helpers into their own modules.

How Has This Been Tested?

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Codex with Pi

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas