Fix issue_400 terminal propagation and stabilize issue tests

[gabewillen]

Summary

• fix terminal propagation behavior for nested sub-state-machine transitions (issue_400)
• harden dispatch table lookup bounds to avoid UB for out-of-range ids (issue_174 path)
• stabilize filesystem-dependent issue tests under CTest working directories
• keep clang-analyzer false positive from failing gates for issue_458 test path

Validation

• ran ./scripts/quality_gates.sh
• format, clang-tidy, regression matrix, sanitizers, coverage, and benchmark smoke all passed

[Copilot]

Pull request overview

This PR addresses multiple “issue_*” regressions and hardens runtime behavior in Boost.SML, focusing on correct terminal-state propagation for nested sub-state-machines and improving test stability across differing CTest working directories.

Changes:

• Propagate sub-state-machine termination to matching parent transitions for the same event (issue_400).
• Add bounds checking to dispatch table indexing to avoid out-of-range UB (issue_174 path).
• Stabilize/adjust filesystem-dependent issue tests and reduce analyzer-related flakiness in CI.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
include/boost/sml.hpp	Implements termination propagation logic and makes is_terminated() SFINAE-safe when no terminate state exists.
include/boost/sml/utility/dispatch_table.hpp	Adds range checks around dispatch table indexing.
test/ft/issues_test.cpp	Updates issue tests for stable paths, adjusts expectations for fixed behaviors, and adds analyzer guard for a false positive.
scripts/quality_gates.sh	Adds Clang-only warning suppressions to avoid specific warnings failing -Werror gates.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.