Record the amount of time spent in row serialization and deserialization

[joshua-spacetime]

For example, in the case of iter_by_col_eq we want to measure the time spent here

SpacetimeDB/crates/core/src/host/instance_env.rs

Lines 264 to 266 in 331b1d8

	for result in results {
	bsatn::to_writer(&mut bytes, result.view()).unwrap();
	}

We can either measure the serialization time directly or the entire time of the syscall, including the row serialization time.

[joshua-spacetime]

We already record the time of each syscall which includes both serialization and copying data into wasm memory. At this point we probably don't need to get more fine grained than that.