refactor: Brush up repo for publishing (pt. 3)

[slowli]

What ❔

• Documents all public items, applies the corresponding lint.
• Applies more clippy lints.
• Makes snapshot management private. Makes some more types / traits private as well (e.g., PtrOp trait).
• Exposes Snapshot and StorageChange types.
• Re-exports zksync_vm2_interface as the interface module instead of re-exporting its items.
• Removes potential UB during offset_from calls.

Why ❔

Part of preparations for publishing the VM.

Checklist

• PR title corresponds to the body of PR (we generate changelog entries from PRs).
• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• Code has been formatted via cargo fmt and cargo clippy.

[slowli]

• Can split the PR into parts if it makes it more reviewable.
• There are some debatable decisions (e.g., enabling pedantic clippy lints – I think it makes code better, but this is subjective).
• The built crate docs are available.

[slowli]

Here's the corresponding PR on the Era side: matter-labs/zksync-era#2883. There's performance regression on some iai benches (order of 2–3%); will investigate its cause.

[joonazan]

Looks good once the remaining few comments are implemented.

I will fix the invalid instruction unsoundness in a separate PR.