Improve oak functions benchmarks

[tiziano88]

cc @waywardgeek

[tiziano88]

cc @andrisaar

[tiziano88]

@pmcgrath17

[tiziano88]

I am modifying the existing bench.

Somewhat interesting results.

For an echo Wasm module:

test wasm::tests::bench_invoke_echo   ... bench:      88,085 ns/iter (+/- 6,912)

For a k/v lookup Wasm module that does a single lookup:

test wasm::tests::bench_invoke_lookup ... bench:     104,695 ns/iter (+/- 9,098)

If I increase the number of lookups to 100:

test wasm::tests::bench_invoke_lookup ... bench:   1,685,143 ns/iter (+/- 556,036)

And to 1,000:

test wasm::tests::bench_invoke_lookup ... bench:  15,497,293 ns/iter (+/- 584,814)

And to 10,000:

test wasm::tests::bench_invoke_lookup ... bench: 155,914,223 ns/iter (+/- 14,439,435)

So, it seems to scale roughly linearly, as we would expect naively.

But now I would like to see if @waywardgeek 's suggestion of introducing batching, but at the Wasm lookup logic level, makes things any better.