Speed up building and running of tests

[sbillig]

What was wrong?

Tests take a long time to run.

How was it fixed?

Mostly by telling cargo to build solc with optimizations for dev builds. I also moved the integration tests into a single module (and thus a single binary), to cut down on the time spent linking the test binaries, removed some dependencies and updated the rest.

In practice, this will slow down the build of solc in favor of much faster test execution. I'm not exactly sure by how much, because I'm sick of timing builds :). If solc is built using sccache (which will now happen automatically, if sccache is installed), then every build after the first will be much faster than it was prior to this pr.

Times on my laptop, before:
(with rust artifacts cached via sccache, but not solc because it wasn't possible/easy prior to g-r-a-n-t/solc-rust#2)

cargo clean && cargo test --workspace --all-features: 687s
cargo test --workspace --all-features: 85s

after:
(with rust and solc cached via sccache)
cargo clean && cargo test --workspace --all-features 176s
cargo test --workspace --all-features 18s

[codecov-commenter]

Codecov Report

Merging #383 (9de205a) into master (2960a12) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #383   +/-   ##
=======================================
  Coverage   86.30%   86.30%           
=======================================
  Files          67       67           
  Lines        4032     4032           
=======================================
  Hits         3480     3480           
  Misses        552      552           

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[cburgdorf]

Looks good. You know a whole lot of tricks and tools man 👍