The constructor did not take care of them and our unit tests exposed
that, at least within unit tests, we were accessing uninitialised
members.

Shared pointers may be updated in yet-to-be-executed threads.

`goto_symex_statet` holds a reference to a language mode, which was
being initialised to `goto_symext::language_mode` in
`goto_symext::initialize_entry_point_state`. That `goto_symext` object,
however, may be the one created in
`single_path_symex_only_checkert::initialize_worklist`, whereupon the
`goto_symex_statet` will outlive it.

Fix this problem by getting rid of the `language_mode` member of
`goto_symext` and initialise `goto_symex_statet::language_mode` from a
mode in the symbol table, which outlives all goto-symex objects.

Use mp_integer to compute the number of permitted objects as the number
of object bits is related to the analysis target platform and need not
be within the analysis-execution platform's limits.

Use mp_integer to compute the number of permitted objects as the number
of object bits is related to the analysis target platform and need not
be within the analysis-execution platform's limits.

Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>

The message_handler member of bv_refinementt::infot was left
uninitialised, which is undefined behaviour when it is later
dereferenced. Set it to null_message_handler.

Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>

The test invokes a non-existent binary, which does not terminate
reliably when running under the address sanitizer. Tag it [not_ubsan]
so that the sanitizer CI job can skip it.

Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>

The eval_expr function in cover_instrument_mcdc.cpp dereferences the
result of std::map::find() without checking for end(). This happens
when values_of_atomic_exprs skips inconsistent expressions (where
signs.size() != 1), leaving them absent from the map. When eval_expr
later encounters such an expression, find() returns end() and the
dereference is undefined behavior (stack-buffer-overflow detected by
AddressSanitizer).

Fix by checking the iterator before dereferencing.

Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>

Adds a dedicated CI workflow that compiles with Clang's AddressSanitizer
and UndefinedBehaviorSanitizer, then runs the full test suites. Leak
detection is disabled for now as there are too many reports to address at
once.

The workflow is structured as a build job followed by four parallel test
jobs: unit tests, CBMC regression, CBMC special regression (paths-lifo,
cprover-smt2), and JBMC regression. Build artifacts are shared via a
tarball upload.

The unit test runner skips tests tagged [!shouldfail] and [not_ubsan] in
the main run, then separately runs the expected-failure tests.

- [AddressSanitizer](https://clang.llvm.org/docs/AddressSanitizer.html)
- [UndefinedBehaviorSanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html)

Fixes: diffblue#832

Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>