Change parameter type of sleep and other functions to fix #15313

[Dutcho]

Change accepted parameter type of sleep and other functions to fix #15313

This changes to:

def ctime(seconds: _SupportsFloatOrIndex | None = None, /) -> str: ...
def gmtime(seconds: _SupportsFloatOrIndex | None = None, /) -> struct_time: ...
def localtime(seconds: _SupportsFloatOrIndex | None = None, /) -> struct_time: ...
def sleep(seconds: _SupportsFloatOrIndex, /) -> None: ...

For Python <= 3.14, _SupportsFloatOrIndex is a little white lie: It aliases float | SupportsIndex. However, that prepares for Python >= 3.15, when it will correctly name the alias.

[Dutcho]

Diff from mypy_primer, showing the effect of this PR on open source code:

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/deployments/flow_runs.py:441: error: Argument 1 to "sleep" has incompatible type "float | None"; expected "float"  [arg-type]
+ src/prefect/deployments/flow_runs.py:441: error: Argument 1 to "sleep" has incompatible type "float | None"; expected "float | SupportsIndex"  [arg-type]

I'd consider this diff as by intent.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/deployments/flow_runs.py:441: error: Argument 1 to "sleep" has incompatible type "float | None"; expected "float"  [arg-type]
+ src/prefect/deployments/flow_runs.py:441: error: Argument 1 to "sleep" has incompatible type "float | None"; expected "float | SupportsIndex"  [arg-type]