BREAKING CHANGE: Pickle deserialization now only permits safe built-in
types (builtins, collections, datetime, decimal, fractions, uuid).
Arbitrary objects can no longer be deserialized from cache, preventing
code execution via crafted pickle payloads.

Users caching custom types should migrate to JSONDisk or a custom Disk
subclass. There is no opt-out mechanism by design.

- Add SafeUnpickler with allowlist-based find_class override
- Add UnpicklingError (inherits pickle.UnpicklingError) for downstream
  compatibility with libraries catching pickle.PickleError
- Support pickle protocols 0-5 via __builtin__, copy_reg, and _codecs
  allowlist entries
- Use frozenset values in SAFE_PICKLE_CLASSES to prevent runtime bypass
- Bump version to 6.0.0 (breaking change per semver)

This takes a different approach to PR #361 (HMAC envelope). The HMAC
approach still allows arbitrary deserialization once the signature is
verified, meaning an attacker with read+write access to the cache
directory can read the auto-generated key file and forge valid
payloads. The allowlist approach blocks dangerous types regardless of
filesystem access.

Fixes: CVE-2025-69872
Closes: #357, #360, #362

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

…strictions

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Fix CVE-2025-69872: restrict pickle deserialization to safe types

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(#868k5bbdr): Publish on push to master

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(#868k5bbdr): Set releasesBranch=master, use PEP 440 version output

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(#868k5bbdr): Grant contents:write for action-vtl to create tags

…merges

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

docs(#868k5bbdr): Add fork notice — temporary CVE fix until upstream merges

…ride

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(#868k5bbdr): Rename package back to diskcache for git source override