Add tracing::debug_span calls throughout runtime

[matklad]

In #4038 we added some basic tracing support for runtime. We should complete that work and add enough spans to all the critical code-paths to get a full picture of runtime performance.

For example, right now I am debugging an estimator issue, and I am looking at the following trace:

2.01ms Runtime::process_receipt 140.25µs run_vm 134.64µs run_wasmer2 1.24µs get_key 54.26µs deserialize_wasmer2 32.21µs run_method 27.67µs run_method/instantiate 500.00ns run_method/call 1.10µs run_method/drop_instance

It would be really great to understand where those extra 1.860ms of time went!

cc @nikurt

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[nikurt]

Related to #6731

[exalate-issue-sync]

Nikolay Kurtov commented:

Experimenting with the tracing data shows that all important pieces are annotated with tracing::debug_span or tracing::trace_span.