[CHORE] Replace bincode (unmaintained) with a maintained serialization crate

[ElioNeto]

Description

cargo audit reports bincode v1.3.3 as unmaintained (RUSTSEC-2025-0141). The crate is used extensively throughout ApexStore for serializing WAL records, SSTable metadata, and more.

Impact

• No security fixes for future vulnerabilities in bincode
• No performance improvements
• Risk of relying on unmaintained serialization in a storage engine

Recommendation

Evaluate replacements:

• bincode v2.x (if stable)
• postcard (no_std, binary, fast)
• msgpack via rmp-serde
• Custom compact encoding for WAL/SSTable formats

Severity

Medium — no known vulnerability in current bincode version, but unmaintained status is a risk.

Labels

[ElioNeto]

Fixed in commit 0a75fb2. Replaced unmaintained bincode with postcard.