Release v0.10.2

Fix Result double-wrapping bug in CustomNode.Exec

When using NewNode with WithExecFunc and WithPostFunc, Result.Bind() was
failing silently because execResult was being double-wrapped. The user's
execFunc returns a Result, but CustomNode.Exec was returning that Result
directly (as any), then CustomNode.Post was wrapping it again with
NewResult(), causing Result{value: Result{value: actualData}}.

This fix unwraps the Result in CustomNode.Exec before returning (similar
to how Prep already unwraps). Error Results are preserved to maintain
batch processing behavior.

- Modified CustomNode.Exec to unwrap Result.Value() before returning
- Special handling for error Results to preserve batch error tracking
- Added tests to verify Result.Bind() works in ExecFunc and PostFunc
- Updated builder tests to reflect new behavior