Fix parallelism bug in exit processing (#1110)

* Fix parallelism bug in exit processing

Also:

* Remove parallelism for all other operations except deposit merkle proofs
* Improve exit tests
* Fix broken attestation test

Closes #1090

* Allow for generating block/pre/post states from some unit tests (#1123)

* Add post-state checks, comments

* Add state_transition_vectors crate

* Integrate new testing crate with CI

* Add readme

* Add additional valid tests

* Remove ExitTests (they were moved to new crate)

* Small test fixes

* Delete incorrect saturating_sub in slash_validator

And clean-up the balance increase/decrease functions to look more like the spec.

Co-authored-by: Paul Hauner <paul@paulhauner.com>

Makefile

@@ -1,6 +1,7 @@
 .PHONY: tests
 
 EF_TESTS = "tests/ef_tests"
+STATE_TRANSITION_VECTORS = "tests/state_transition_vectors"
 
 # Builds the Lighthouse binary in release (optimized).
 #
@@ -35,6 +36,10 @@ run-ef-tests:
 	cargo test --release --manifest-path=$(EF_TESTS)/Cargo.toml --features "ef_tests"
 	cargo test --release --manifest-path=$(EF_TESTS)/Cargo.toml --features "ef_tests,fake_crypto"
 
+# Runs only the tests/state_transition_vectors tests.
+run-state-transition-tests:
+	make -C $(STATE_TRANSITION_VECTORS) test
+
 # Downloads and runs the EF test vectors.
 test-ef: make-ef-tests run-ef-tests
 
@@ -66,3 +71,4 @@ arbitrary-fuzz:
 clean:
 	cargo clean
 	make -C $(EF_TESTS) clean
+	make -C $(STATE_TRANSITION_VECTORS) clean