declare timeout ini options as float

[zxyasfas]

Fixes #194.

With pytest 9's native [tool.pytest] table, timeout = 1200 (a TOML int) makes the whole session die at configure time:

INTERNALERROR> TypeError: pyproject.toml: config option 'timeout' expects a string, got int: 1200

because timeout and session_timeout are registered with the default string ini type. Registering them with type="float" fixes it, matching what the values actually are. Legacy [pytest] ini strings like timeout = 2.5 still parse the same way, and timeout = 0 still means disabled (the > 0 checks are unchanged).

One catch: type="float" was added to addini in pytest 8.4, and registering it under 8.0.x fails at plugin load, so this bumps the floor in setup.cfg to pytest>=8.4.0. If keeping 8.0 support matters more, the alternative is a try/except shim around the registration; happy to switch if you prefer that.

Added a regression test using makepyprojecttoml with int values for both options (skipped below pytest 9, where the native table doesn't exist). Suite passes locally on 3.12: 35 passed, 21 skipped (the pexpect spawn skips, this is a Windows machine).

[flub]

Thanks!