refactor!: more conventional marshaling

This commit refactors marshaling API. It has two objectives:

- Align how marshaling works with conventional Go practices, ensuring
  new users familiar with other Go libraries have minimal surprises.
- Minimize the impact of marshaling on IClaims interface, relieving the
  burden on current and future implementations.

To that end, the following changes are made:

- From/To* marshaling API are replaced with implementations of standard
  cbor and json marshaling interfaces (i.e. Unmasrshal/Marshal*). As per
  convention, these implementations do not validate.
- There are no validating versions of marshaling methods (thus no
  requirement for every IClaims implementation to re-implement them).
  Instead, there are convenience functions that instantiate, marshal,
  and validate in a single call.
- The functions have been renamed such that Decode* now only performs
  unmarshaling, and DecodeAndValidate* unmarshals and validates.
- Decoding/Encoding functions for IClaims have been moved from
  profile.go to iclaims.go.

note: this is implemented on top of a similar refactor inside psatoken

BREAKING CHANGE: the From/To marshaling API have been removed; Decode*
functions have been renamed to be consistent with marshaling (rather
then DecodeXXX--that validates--and DecodeUnvalidatedXXX, there is now
DecodeAndValidateXXX and DecodeXXX--that does not validate).

Signed-off-by: Sergei Trofimov <sergei.trofimov@arm.com>

.github/workflows/ci-go-cover.yml

@@ -14,7 +14,7 @@
 # 1. Change workflow name from "cover 100%" to "cover ≥92.5%". Script will automatically use 92.5%.
 # 2. Update README.md to use the new path to badge.svg because the path includes the workflow name.
 
-name: cover ≥85.0%
+name: cover ≥83.1%
 on: [push, pull_request]
 jobs:
   cover: