fix(dnsserver): Fix SOA record timeout issue by correcting RRSIG field formatting
- Fixed RRSIG generation by using correct field name 'signersName' (not 'signerName')
- Fixed label count calculation in RRSIG by filtering empty strings
- Added SOA records to DNSSEC signing map for proper RRSIG generation
- Added error logging and fallback values for RRSIG generation robustness
- Updated test expectations to match corrected DNSSEC RRset signing behavior
- Added comprehensive SOA test coverage including timeout, debug, and simple test scenarios