fix: allow description field to be absent from `Tool`#159

mattt merged 3 commits intomodelcontextprotocol:mainmodelcontextprotocol/swift-sdk:mainfrom

abcsnowwolf:fix/description_is_not_a_required_fieldabcsnowwolf/swift-sdk:fix/description_is_not_a_required_fieldCopy head branch name to clipboard