Fix: from_reader() multibyte varint parsing

[sumanjeet0012]

Closes #67

Description

This PR fixes an issue where from_reader() incorrectly parsed CIDv1 when dealing with multihash types or lengths that use multi-byte varints (e.g., blake2b-256 which has the code 0xB220).

Previously, the parsing logic assumed that the multihash code and digest length were always precisely 1 byte, leading to ValueError: Not enough data to read CIDv1 multihash when decoding multi-byte codes.

Changes

• Imported varint to correctly decode varint integers incrementally from the stream.
• Replaced the hardcoded single-byte array reading logic with varint.decode_stream by implementing an internal TrackingReader that properly counts bytes consumed.
• This ensures full compatibility with CIDs containing any arbitrary multicodec and multihash varint combinations.