Limit CBOR depth

[maxtropets]

Parsing CBOR of undefined depth or roughly 10k+ can overflow. This PRs adds a safety barrier to only parse reasonably deep CBORs, while still allows to go deeper with a newly added function parameter.

[Copilot]

Pull request overview

Adds a configurable nesting-depth limit to the internal CBOR parser/serializer to prevent stack overflow from adversarially (or accidentally) deeply-nested CBOR, with coverage in the CBOR unit tests.

Changes:

• Add max_depth parameter (default 16) to ccf::cbor::parse and ccf::cbor::serialize.
• Enforce depth checks during CBOR decode (consume*) and encode (to_raw_*) recursion, throwing on exceed.
• Add unit tests validating parse/serialize behavior at and beyond configured depth limits.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/crypto/cbor.h	Extends CBOR parse/serialize API with a max_depth parameter (default 16).
src/crypto/cbor.cpp	Implements max-depth enforcement in recursive decode/encode helpers.
src/crypto/test/cbor.cpp	Adds tests for max-depth behavior in parsing and serialization.