feat: multibase integration

[asmit27rai]

Multibase Integration

Integration of py-multibase into py-libp2p.

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Phase-wise Plan

Phase 1: Add Multibase Support (Completed)

• Add py-multibase as a dependency.
• Extend Peer ID class with multibase encode/decode methods (backward compatible).
• Add multibase-aware utility functions for DHT keys.
• Update pubsub message ID encoding to use multibase.
• Preserve legacy base58/base64 support for compatibility.
• Add and update tests for multibase, compatibility, and error handling.

Phase 2: Internal Migration (Upcoming)

• Migrate internal code to use multibase by default.
• Update peer ID parsing, DHT, and pubsub internals.
• Update examples and documentation.

Phase 3: External API & Config (Upcoming)

• Consider making multibase the default for external APIs.
• Provide configuration for encoding preferences.

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Testing

• All new and existing tests pass for Phase 1, including backward compatibility and error handling for both multibase and legacy base58.