Make infiniteGas default, add setGas cheatcode

[palinatolmach]

Closes runtimeverification/kontrol#38 and #2058 (infinite gas prevents setUp from branching on potential out-of-gas caused by SSTORE-ing a symbolic value).

This PR makes the following changes:

• Turns on infinite gas by default, thereby improving the default performance of Kontrol on Foundry proofs;
• Adds kevm.setGas(uint256) cheatcode that allows setting the available gas; adds a test for it (GasTest.testSetGas);
• Removes kevm.infiniteGas() from tests, as it's no longer necessary;
• Modifies test_foundry_merge_nodes, LoopsTest.sum_N and the associated loop invariant accordingly (adding or removing gas-related cheatcodes changes program counter values and node numbering, which are hardcoded in these two tests).

[ehildenb]

This PR should be migrated to the new Kontrol repo: runtimeverification/kontrol, instead.

[palinatolmach]

@ehildenb Kontrol-specific changes have been moved to runtimeverification/kontrol#57. This PR includes changes to foundry.md which has not been moved to the Kontrol repo yet (issue: runtimeverification/kontrol#61) and duplicates other changes in kontrolx and tests. After a discussion with @tothtamas28, we decided that we might merge this PR first before foundry.md is transferred to Kontrol, and refactor later, if necessary.

[palinatolmach]

Closed in favor of the Kontrol PR (runtimeverification/kontrol#57) and a smaller foundry.md change (#2101).