fix(client): add metadata parameter to score_current_span and score_current_trace (#1501)

Added optional metadata parameter to both score_current_span and
score_current_trace methods to allow attaching additional context
to scores. This brings these convenience methods to feature parity
with the underlying create_score method which already supports metadata.

Changes:
- Added metadata parameter to all overloads of score_current_span
- Added metadata parameter to all overloads of score_current_trace
- Updated docstrings with metadata parameter documentation
- Updated examples to demonstrate metadata usage
- Passed metadata parameter through to create_score calls