Consensus: reject wrapped Spark name validity

[cursor]

PR intention

Fix a critical Spark-name consensus validation bug where crafted sparkNameValidityBlocks values near UINT32_MAX could wrap when converted to signed int, bypassing max-validity checks and underflowing fee-year calculation.

Code changes brief

• Use 64-bit unsigned arithmetic for Spark-name purchased/total validity checks and expiration carry-over.
• Avoid signed sentinel arithmetic for existing expiration heights.
• Add a regression test covering a wrapped validity value that must be rejected from mempool/block validation.

Validation performed:

• git diff --check HEAD~1..HEAD
• Attempted headless test configure: CC=/usr/bin/gcc CXX=/usr/bin/g++ cmake -G Ninja -DBUILD_GUI=OFF -DWITH_ZMQ=OFF -DBUILD_TESTS=ON -S /workspace -B /workspace/build (blocked by missing Boost 1.81+ components in the environment).