fix(genesis): reject zero block gas limit

[huklaa]

Fixes #321.

Aligns genesis ProtocolConfig validation with the runtime protocol config invariant by requiring blockGasLimit to be at least 1 instead of allowing zero.

Adds focused schema regression coverage verifying that:

• blockGasLimit: 1n is accepted
• blockGasLimit: 0n is rejected
• values above uint64 are rejected

This keeps genesis configuration from accepting a value that the runtime mutative API would reject.

[kutluhaneth46]

Heads-up: this looks like a duplicate of #327 (same one-line blockGasLimit: schemaBigInt.min(1n) change for #321). #327 also adds unit coverage under a different test filename. Worth coordinating so maintainers only merge one — happy to close this in favor of #327 if that helps triage.

[huklaa]

Closing this in favor of #327, which already implements the same #321 fix and focused boundary coverage. Keeping only one patch avoids duplicate review/merge work for maintainers. Thanks for the heads-up.

[kutluhaneth46]

Sounds good — thanks for closing in favor of #327. Agreed that keeping a single patch is cleaner for review.