Avoid mutate Integer.value at a few more places, remove sig_occurred() check in Integer fast_tp_dealloc

[user202729]

Follow-up to #40556. Now the sig_occurred() check in fast_tp_dealloc is removed.

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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)

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

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