Resolve spec-wide PURL encoding issues

[johnmhoran]

We have a number of open issues and PRs that involve character encoding, which could be handled one-by-one or as a group, in any event likely including an update/clarification of the core spec encoding section. (Encoding is also discussed in other sections of that file as well as for various defined types.)

Please share your views on how we can best address this set of encoding-related issues/PRs.

• PR Update Test Suite #52 (asks about encoding of ":", "/" and other characters)
• PR docs(types): oci type repositry_url must be parcent encoding #150 (concerns encoding of the repository_url value)
• PR add an example with / in namespace to README and SPEC #176 (asks about encoding "/" in a namespace)
• PR Revert "Fix missing percent-encoding in purl example with repository_url" #184 (involves percent-encoding of the "/" in an example repository_url value) -- this was merged by sschuberth on 2024-11-21
• PR feat(test-suite-data): add test case for checksum qualifier #207 (has a test with a download_url qualifier containing multiple unencoded "/")
• PR define handling of plus and space #261 (involves encoding for qualifiers (here it's space ' ' and plus sign '+'))
• issue Clarifications #35: (character encoding)
• issue Percent encoding spec and : and / #39 (asks when ':' and '/' should/should not be encoded)
• issue Update Test Suite #52: (encoding of ":" in test object version)
• issue clarify handling of "+" (plus) sign and blanks (spaces) #58: (encoding of "+" and " ")
• issue Inconsistency in the description of the checksum qualifier. #73 (asks when a checksum qualifier should be encoded including ":")
• issue Drop the notion of namespace from PackageURL #204 (encoding, or not, of slashes in a namespace)