Function from_msgpack 

pub fn from_msgpack(
    _msgpack: &[u8],
    _plan: &ExecutionPlan,
) -> Result<HashMap<String, LiteralValue>, LemmaError>

Convert MsgPack values to typed Lemma values using the ExecutionPlan for type information.

MsgPack preserves type information (int, float, bool, string, etc.), allowing validation that values are compatible with expected Lemma types.

This is a stub implementation. Full MsgPack support requires:

1. Add rmp-serde dependency
2. Deserialize MsgPack to intermediate format
3. Validate MsgPack types against expected Lemma types
4. Convert to LiteralValue directly