Improve performance of `find_max_char`

Feature or enhancement

Proposal:

find_max_char is called each time a string is created.
By reducing the amount of tests, the performance can be improved considerably.

python -m pyperf timeit -s "b=('a' *1000+ '\u019f'*2)" "b[:-1]"

+-----------+--------+----------------------+
| Benchmark | ref    | patch                |
+===========+========+======================+
| timeit    | 442 ns | 388 ns: 1.14x faster |
+-----------+--------+----------------------+

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-122902

首先在 CPython 中找到 find_max_char 的实现，并使用当前行为运行所提供的 pyperf 命令。将基准测试结果与报告中的 442 ns 参考值和 388 ns 补丁结果进行比较；当精简后的测试方法在不改变字符串创建行为的情况下提升性能时，即表示完成。