chore: unify word and array attachment into one

[PhilippGackstatter]

Addresses various follow-up issues from the previous attachment PRs:

• Unify attachment word and array variants into a single NoteAttachmentContent.
• In NoteAttachment rename new_word -> with_word & new_array -> with_words.
• Refactor add_array_attachment to add_words_attachment which takes a ptr and num words as input.
• Make NoteHeader and NoteMetadata Copy (as it was before note attachments were added to metadata).
• Add dedicated error for total num words exceeded.
• Move attachment tests to dedicated module.
• Enforce total number of attachment words per note in kernel (already implemented in Rust).
• Add test to check exceeding max attachment count and max total elements aborts as intended.
• Create shared constants.masm for WORD_NUM_ELEMENTS (named as per the upcoming refactor(Word): Make Word constants consistent crypto#917).
• Update attachment docs in note.md.
• Reorder memory layout of output notes to place single-element data into the same word.
• Implement metadata_into_tag and use it in PSWAP code. See issue TODO for the motivation behind this procedure.
• Support multiple attachments in send_note (see also feat: implement setting multiple note attachments #2795).
  • This uncovered a padding bug in add_attachment that was fixed.

closes #2555

[bobbinth]

Looks good! Thank you! I left a few small comments inline. Not approving yet as things may change a little depending on what we do in the base PR.