gh-40734: Avoid mutate Integer.value at a few more places, remove sig_occurred() check in Integer fast_tp_dealloc
    
Follow-up to #40556. Now the `sig_occurred()` check in `fast_tp_dealloc`
is removed.

------

This is the effect on the last commit, changing `divisors()` to use
`sig_check()`.

Before:

```
sage: n = prod(primes_first_n(17))
....: %timeit ignore = n.divisors()
20 ms ± 245 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
sage: n = prod(primes_first_n(17))
....: %timeit ignore = n.divisors()
20.5 ms ± 616 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
sage: n = prod(primes_first_n(17))
....: %timeit ignore = n.divisors()
20 ms ± 302 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
```

After:

```
sage: n = prod(primes_first_n(17))
....: %timeit ignore = n.divisors()
20.6 ms ± 424 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
sage: n = prod(primes_first_n(17))
....: %timeit ignore = n.divisors()
20.5 ms ± 254 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
sage: n = prod(primes_first_n(17))
....: %timeit ignore = n.divisors()
20.7 ms ± 206 μs per loop (mean ± std. dev. of 7 runs, 10 loops each)
```


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### ⌛ Dependencies

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URL: #40734
Reported by: user202729
Reviewer(s):

Author: Release Manager

src/sage/libs/gmp/mpz.pxd

@@ -6,7 +6,7 @@ from libc.stdio cimport FILE
 
 from libc.stdint cimport intmax_t, uintmax_t
 
-cdef extern from "gmp.h":
+cdef extern from "gmp.h" nogil:
 
     ### Integer Functions ###