fix: fix handling of floating point values for connect_timeout

[dvarrazzo]

The connect_timeout parameter is specified as integer.

It seems that certain libpq versions handle correctly a floating point connect timeout:

$ psql connect_timeout=5.0
psql (11.22 (Debian 11.22-0+deb10u2), server 16.2)
WARNING: psql major version 11, server major version 16.
         Some psql features might not work.
Type "help" for help.

others don't

$ psql --version
psql (PostgreSQL) 16.2 (Ubuntu 16.2-1.pgdg22.04+1)
$ psql "connect_timeout=5.0"
psql: error: connection to server on socket "/var/run/postgresql/.s.PGSQL.5432" failed: invalid integer value "5.0" for connection option "connect_timeout"

Psycopg doesn't, but mostly by accident, and in the recent version where the connection timeout and the multiple attempts are taken more care of:

$ python -c "import psycopg; psycopg.connect('connect_timeout=5.0')"
Traceback (most recent call last):
  File "/home/piro/dev/LiveSurface/BackSurface/.venv/lib/python3.10/site-packages/psycopg/conninfo.py", line 141, in timeout_from_conninfo
    timeout = int(value)
ValueError: invalid literal for int() with base 10: '5.0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/piro/dev/LiveSurface/BackSurface/.venv/lib/python3.10/site-packages/psycopg/connection.py", line 727, in connect
    timeout = timeout_from_conninfo(params)
  File "/home/piro/dev/LiveSurface/BackSurface/.venv/lib/python3.10/site-packages/psycopg/conninfo.py", line 143, in timeout_from_conninfo
    raise e.ProgrammingError(f"bad value for connect_timeout: {value!r}")
psycopg.ProgrammingError: bad value for connect_timeout: '5.0'

it seems safe to parse a floating point error too.

[dvarrazzo]

To be clearer, this can be considered a regression, because in previous implementations of psycopg a float was accepted ok. I found the problem because a program of mine failed to start after a libraries upgrade.