Panic on cache initialization if size is zero

[qj0r9j0vc2]

Several cache initializations panic if the cache size is somehow zero.

Locations:

• https://github.com/decipherhub/cipherbft/blob/main/crates/execution/src/database.rs#L20
• https://github.com/decipherhub/cipherbft/blob/main/crates/execution/src/database.rs#L26
• https://github.com/decipherhub/cipherbft/blob/main/crates/execution/src/state.rs#L20
• https://github.com/decipherhub/cipherbft/blob/main/crates/execution/src/engine.rs#L30

While the constants are non-zero, these panics could be replaced with compile-time assertions or graceful error handling.