`_get_tag()` missing 6 tags present in go-multicodec

[sumanjeet0012]

The _get_tag() function in code.py is missing 6 codec category tags that exist in the Go reference implementation: multikey, multisig, nonce, shelter, softhash, and vlad. Codecs belonging to these categories currently return "<unknown>" instead of the correct tag.

Problem

The _get_tag() function in multicodec/code.py uses hardcoded pattern matching to classify codecs into category tags. Six tags that exist in the upstream multicodec table.csv and in go-multicodec are not handled:

from multicodec import Code

# These should return specific tags but return "<unknown>" instead:
Code(0xA000).tag()   # chacha20-poly1305 → "<unknown>" (should be "multikey")
Code(0x123B).tag()   # nonce             → "<unknown>" (should be "nonce")
Code(0xCC01).tag()   # iscc              → "<unknown>" (should be "softhash")
Code(0x1207).tag()   # vlad              → "<unknown>" (should be "vlad")

# All multisig codecs (es256k-msig, eddsa-msig, etc.) → "<unknown>" (should be "multisig")
# All shelter codecs (shelter-contract-*, shelter-file-*) → "<unknown>" (should be "shelter")

Proposed Solution

Add the 6 missing tag categories to _get_tag() in multicodec/code.py:

1. multikey — match "chacha20-poly1305"
2. multisig — match names containing "-msig" or "lamport-" with "-sig" suffix patterns
3. nonce — match "nonce"
4. shelter — match names starting with "shelter-"
5. softhash — match "iscc"
6. vlad — match "vlad"

Add corresponding tests in tests/test_code.py for each new tag.

Related

• Go implementation: go-multicodec code_table.go Tag() method
• Upstream table: multicodec/table.csv