calculate sig ops on fly

[biryukovmaxim]

Migrate to runtime signature operation counting

Changes signature operation counting from static analysis to runtime counting during script execution for improved accuracy.

Key changes

• Add sig_op tracking fields to TxScriptEngine
• Remove static sig_op counting functions
• Count sig_ops during script execution
• Add runtime checks for sig_op limits
• Add new error type for sig_op limit violations
• Update transaction validation to use runtime counting

Breaking changes

• Changes sig_op validation timing from pre-execution to during execution
• May affect transaction fee estimation

Todo

• Restore and update test_get_sig_op_count tests
• Add tests for sig_op limit edge cases and errors
• Decide approach for P2SH sig_op limits in mempool standardness rules
• Add documentation for new sig_op runtime counting behavior
• Consider adding sig_op estimation helper for fee calculation

Requires manual testing and careful review of sig_op counting logic.