Provides assert_true/false, assert_eq, assert_int_eq, assert_neq,
assert_contains, assert_starts_with, assert_ends_with, and fail.
Test cases are registered by name+fn_name, executed sequentially via
the thread/dlsym dispatch mechanism, with results tracked in state_.
Includes tests/runtime/string_test.el covering all 23 string.el exports.
Will Anderson