Pass decomposition expr to a lambda instead of storing it to a local

[sarah-quinones]

i first ran into this bug while using libassert with eigen, which uses expression templates (not very well imo)
writing code like this

void compare(Eigen::MatrixXd a, Eigen::MatrixXd b) {
    LIBASSERT_ASSERT(a * a * a == b);
}

results in undefined behavior, because the a * a produces a temporary that contains references to a, which is then referenced by the expression holding (a * a) * a.
if you store this to a local then the lifetime of that temporary is ended by the time the comparison is actually evaluated, resulting in undefined behavior

my suggested fix is to replace do { auto expr = decomposition; } while (0) with [&](auto expr) { ... } (decomposition), but let me know if you have a different solution