Add boundary advance helper

[tradingexpert]

Summary

• add BoundaryAdvance and advance_until_fill_boundary(...) as the Python bridge for fill-boundary advancement
• use the compiled C++ boundary method when compiled columns are available, with scalar fallback for the Python reference engine
• document that this is the tested bridge before changing ordinary Replay semantics

Tests

• python -m ruff check .
• python -m pytest
• mkdir -p build/cpp && c++ -std=c++17 -Wall -Wextra -pedantic -Icpp cpp/tests/matching_engine_core_test.cpp -o build/cpp/matching_engine_core_test && build/cpp/matching_engine_core_test

Coverage: 98.17% total.