Refactor code to move all store specific functionality into the store implementations

[schmidtfx]

At the moment, store specific functionality is spread across the code base, e.g., path canonicalization. This makes it hard for others to extend the library with additional store implementations.

[midiakiasat]

One thing to be careful about: path canonicalization is not just store-specific plumbing, it is part of the correctness contract.

If canonicalization logic is moved into store implementations, there should still be a single, explicit canonical form defined at the interface boundary (e.g., normalization rules, separators, case handling). Otherwise different stores may legally canonicalize the “same” path differently, leading to divergent behavior across backends.

Recommendation:

• Define the canonical path semantics once (documented and tested).
• Allow stores to implement how they enforce it, but not what the canonical form is.