Recursive user-defined operators (e.g. a `string::/=` whose body calls
itself through string interpolation) drove the AST evaluator into
unbounded native recursion and crashed the host process with SIGSEGV.
The dispatcher now refuses to enter a new function frame once
`Stack_Holder::call_depth` reaches `chaiscript::max_call_depth`
(default 256, overridable via the `CHAISCRIPT_MAX_CALL_DEPTH` macro)
and throws the new `chaiscript::exception::stack_overflow_error`
instead, letting both ChaiScript-level `try`/`catch` and C++ hosts
recover from runaway recursion.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
