Use CBOR wrappers in COSE auth

[maxtropets]

Yet another step towards #7542

Faced difficulties with error handling for optionals, as in

try {
  value = cbor->map_at(KEY)->as_TYPE();
}
catch (CBORError) {
  // ignore because optional ignores ALL errros
  // but we only want to ignore lookup, and still report wrong type or any other error
}

Doing two lookups as in

if (cbor->map_has(KEY)) {
  ...
}

needs reiterating, and simply

Value value;
try {
  value = cbor->map_at();
}
catch {
  // ignore
}

// convert to type with rethrow wrapper

doesn't work, because map_at() returns const T&.

At the end, I decided to categorise errors. Now each has a concrete Error included, which can be used to classify errors and either rethrow or silence.

❗ This changes the existing behaviour for TimestampedProtectedHeader with std::optional<uint64_t> msg_created_at;. Previously, it'd have silently avoid that field if it was negative, however it looks wrong to me, so we'll fail if the filed is present but ill-formed.

[Copilot]

Pull request overview

This PR refactors COSE authentication parsing to use CBOR wrapper APIs instead of direct QCBOR calls. The refactoring introduces structured error categorization through an Error enum and updated CBORDecodeError class, enabling better error handling for optional header fields.

Changes:

• Introduced categorized error handling with Error enum and enhanced CBORDecodeError class
• Replaced QCBOR-based parsing with CBOR wrapper API calls in COSE authentication functions
• Changed validation behavior for TimestampedProtectedHeader.msg_created_at to fail on negative values (previously silently ignored)

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/crypto/cbor.h	Added Error enum and converted CBORDecodeError to a class with error code tracking
src/crypto/cbor.cpp	Updated all error throwing sites to use new error codes and implemented CBORDecodeError class methods
src/endpoints/authentication/cose_auth.cpp	Refactored COSE parsing to use CBOR wrappers with categorized error handling for optional fields