Fix default test selection in the absence of--match-test

[palinatolmach]

Closes #382.

This PR refactors the logic for selecting tests for verification if no --match-test is provided to:

• include tests that start with check and prove, in addition to test, following a similar change in Verify proveX and checkX functions similarly to testX #249
• instead of selecting test contracts ending with Test, verify contracts located in the test folder (by default) or in the one specified in foundry.toml, e.g.

test = 'test/kontrol/proofs'

This seems to be the approach Foundry is using to select tests, e.g., forge test executes tests located in OptimismPortalKontrol (not ending with Test), but doesn't analyze test contracts located in folders other than test:

❯ forge test
...
Running 3 tests for test/OptimismPortal.k.sol:OptimismPortalKontrol
[PASS] test_finalizeWithdrawalTransaction_paused(...) (runs: 256, μ: 81151, ~: 82169)

Adding / to such test directory is needed to ensure that we're matching a folder (not just the test keyword) against the contract path.

[anvacaru]

Approved with a single suggestion!