[dpazj]

Summary

• Decode Metric.properties when converting a received Sparkplug metric into a MessageMetric, instead of always setting properties to None
• Add MessageMetricError::InvalidProperties so malformed property sets (e.g. key/value count mismatches) produce a descriptive error; the metrics iterator logs it and skips the metric, matching srad-app behavior
• Add tests for valid property population and invalid property rejection

Closes the MessageMetric::properties item in the EoN section of TODO.md.

Verification

• cargo test -p srad-eon
• cargo clippy -p srad-eon --all-targets -- -D warnings
• cargo fmt --check