Instantiate all note scripts from libraries instead of programs

[PhilippGackstatter]

After #2502 we should make sure we only construct NoteScripts from libraries, for uniformity. Additionally, there are some small improvements we can make:

• Remove NoteScript::new and convert usages to NoteScript::from_library(_reference).
• Add a test for NoteScript::from_library which is currently unused. Check if there is an opportunity to deduplicate code with NoteScript::from_library_reference.
• Prefer calling NoteScript::from_parts within the from_library* methods so we have a single place where a note script is actually created.
• Remove NoteScript::from_bytes which is unused and delegates to deserialization internally. This is not our usual pattern for deserializing from bytes.

Context: #2502 (comment)

[bobbinth]

I would also add that NoteScript::from_package() should validate that we are constructing the note script from a "note" package (I believe this can be checked via package kind). cc @greenhat and @bitwalker.