Set function counters to zero at startup

[emschwartz]

As discussed in https://github.com/orgs/autometrics-dev/discussions/31, we would like for the function call counter to be initialized to zero, at least in development mode. This is to enable UIs built on top of Autometrics + Prometheus to discover the names of the instrumented functions before the service has received any traffic.

• Spec Function call counter should be initialized to zero #61
• Rust - Initialize counters to zero in debug builds autometrics-rs#119
• Python - Initialize counters at zero autometrics-py#54
• Typescript - Set the function call counters to zero at startup autometrics-ts#88
• C# - Set function call counters to zero at startup autometrics-cs#13
• Java - Set function call counters to zero at startup jamsiedaly/autometricsj#5
• Go - Set function call counters to zero at startup autometrics-go#61

[brettimus]

Do we need to update the queries in the grafana dashboard to make sure the error ratio does not divide by zero? (I know we just removed > 0 from a lot of queries to fix the dashboards, but i think this would only apply to the denominator for the error ratio query)

This caused an issue in the explorer, but grafana might be smarter about handling NaNs

[emschwartz]

@brettimus probably

[P2P-Nathan]

I've taken a look through the C# implementation and this doesn't look feasible with the design, unfortunately.