Fix: decode multi-byte varints correctly in get_prefix

[sumanjeet0012]

Description

Closes #46.

This pull request addresses issue, where get_prefix was returning an incomplete/incorrect prefix for hash functions utilizing multi-byte varint codes (e.g., hash functions with codes > 0x7F like sha2-224, blake2b-*, etc.).

The original code assumed a hardcoded 2-byte prefix size, expecting exactly one byte for the code varint and exactly one byte for the length varint.

Proposed Changes

• Updates get_prefix to properly decode both the hash code varint and the digest length varint from the input stream using BytesIO, guaranteeing accuracy regardless of varint length.
• Adds test cases (test_get_prefix_multi_byte_code & test_get_prefix_type_error) ensuring accuracy against multi-byte codes (using sha2_224 as an example).

[acul71]

Maintainer review (acul71)

Verdict: Request changes

The get_prefix fix looks correct (decode both varints via BytesIO / varint.decode_stream) and addresses #46. Local lint/typecheck/test (230 passed)/docs-ci are green, and there are no merge conflicts with master.

Blocker

• Missing newsfragment: please add newsfragments/46.bugfix.rst (user-facing description, trailing newline).

Optional

• Add a second multi-byte test (e.g. blake2b-256, 3-byte code varint) as cited in #46
• Align TypeError message with decode to include the offending type

Please push the newsfragment and we can re-review for approval.