Improve implementations of UpperExp and LowerExp traits on integers

[GuillaumeGomez]

Follow-up of #128204.

r? @workingjubilee

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

#16 2.903 Building wheels for collected packages: reuse
#16 2.904   Building wheel for reuse (pyproject.toml): started
#16 3.154   Building wheel for reuse (pyproject.toml): finished with status 'done'
#16 3.155   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132715 sha256=dfa09868353292d98f811d3efdb0d54d07389e808efc71d68e3b93c514bf8bec
#16 3.155   Stored in directory: /tmp/pip-ephem-wheel-cache-0flylqbj/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#16 3.158 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#16 3.554 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#16 3.555 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#16 DONE 3.6s
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failures:

---- fmt::num::test_format_int_exp_limits stdout ----
thread 'fmt::num::test_format_int_exp_limits' panicked at core/src/fmt/num.rs:547:5:
attempt to subtract with overflow
---- fmt::num::test_format_int_exp_precision stdout ----
---- fmt::num::test_format_int_exp_precision stdout ----
thread 'fmt::num::test_format_int_exp_precision' panicked at core/src/fmt/num.rs:547:5:
attempt to subtract with overflow

failures:
    fmt::num::test_format_int_exp_limits
    fmt::num::test_format_int_exp_precision

[GuillaumeGomez]

Checked more and it seems like the same strategy cannot be applied here.