PR #200 introduced breaking change - `timeout` value in config is incompatible with older versions

[YuriiMotov]

PR #200 introduced a breaking change: there is no way now to configure timeout in a way compatible with both 2.4.0 and future release (2.5.0 was released and then yanked).

2.5.0 strictly requires float:

INTERNALERROR> TypeError: /home/yurii/code/1.FastAPI/fastapi/pyproject.toml: config option 'timeout' expects a float, got str: '20.0'

while 2.4.0 strictly requires string:

INTERNALERROR> TypeError: /Users/runner/work/fastapi/fastapi/pyproject.toml: config option 'timeout' expects a string, got float: 20.0

[Pierre-Sassoulas]

We had to handle something similar in pytest itself for truncation-limit. (Int or str). We introduced a bunch of typing argparsing helpers that will be available in the latest versions of pytest.