chore(deps): bump libssz crates to 0.3.0

Tracks consensus-specs v1.7.0-alpha.13. The breaking changes in 0.3.0
are confined to progressive containers/lists (EIP-7916 merkleization
roots, the 256-field cap, and unknown ssz attribute keys now being
compile errors), none of which this codebase uses, so no source changes
are required. The release also elides all-zero subtrees and reuses
buffers in merkleize, which is a win on every hash_tree_root we compute.

The lockfile edit is deliberately limited to the four libssz entries: a
full re-resolve additionally repointed leanVM's mt-field/mt-poly at
num-bigint 0.4 and shifted several other duplicate-version picks, which
does not belong in a dependency bump.

Author: MegaRedHand

Cargo.lock

@@ -85,10 +85,10 @@ clap = { version = "4.3", features = ["derive", "env"] }
 leansig = { git = "https://github.com/leanEthereum/leanSig", branch = "devnet4" }
 
 # SSZ implementation
-libssz = "0.2.2"
-libssz-derive = "0.2.2"
-libssz-merkle = "0.2.2"
-libssz-types = "0.2.2"
+libssz = "0.3.0"
+libssz-derive = "0.3.0"
+libssz-merkle = "0.3.0"
+libssz-types = "0.3.0"
 
 # Build-time version info
 vergen-git2 = { version = "9", features = ["rustc"] }