fix: cross-runtime consistency fixes

[sliedig]

Issue number: #82

Summary

Changes

Fixes to align the .NET runtime with Java, Python, and TypeScript for functional equivalence and cross-runtime consistency.

Contracts Service (Unicorn.Contracts)

• ContractEventHandler.cs — CreateContractAsync: renamed metric from "NewContracts" to "ContractCreated" to match the canonical metric name used by all other runtimes
• ContractEventHandler.cs — UpdateContractAsync: added Metrics.AddMetric("ContractUpdated", 1, MetricUnit.Count, MetricResolution.Standard) after a successful UpdateItemAsync call — the update path previously emitted no custom metric

User experience

Before: Contract creation emitted a NewContracts metric (inconsistent with other runtimes). Contract updates emitted no custom metric at all.

After: Contract creation emits ContractCreated and contract updates emit ContractUpdated, consistent with Java, Python, and TypeScript.

Checklist

• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Acknowledgment

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