Update go-verkle serialize proof to match rust-verkle's implementation where each proof of absence contains multiple missing stem.

[eclairss17]

Issue: ethereum/go-verkle#251

Problem

Currently,
go-verkle: 2 missing stems → 1 PoaStem + 2 ExtStatus entries (one per missing stem) ✓
rust-verkle: 2 missing stems → 2 PoaStem entries (duplicated) ✗

Idea

The fix is in go-verkle's SerializeProof, when serializing, the DepthExtensionPresent field needs to duplicate the extension status for each missing stem that shares the same PoA stem, to match rust-verkle's format