Configure non-zero instruction cost in wasm

[sug0]

Bugs in wasm code causing infinite loops and/or dry ran txs with custom wasm code may be a DoS vector, since wasm instructions have no associated gas cost (see get_gas_rules() in crates/namada/src/vm/wasm/run.rs). We should associate some non-zero cost to executing wasm opcodes, in order to avoid the aforementioned problems.

[grarco]

This is a known issue due to the lack of a proper runtime gas meter but I believe two things should be considered:

1. For actual txs in storage we always have the whitelist. This attack can be exploited on loops that don't call host functions (since these are tracking gas). So as long as the whitelist is there and we check what gets whitelisted it should not happen
2. For dry runs this should be fixed in Fix allowlist checks #2819 since the whitelist check is moved inside the call to tx which is called from apply_wasm_tx

Still I'll try to see how hard it is to swap the current whitelist-based gas metering system with a proper runtime one