Split config sections based on entire line

[marksteward]

Currently you'll get the following error if parsing a config file with a commented out peer:

Traceback (most recent call last):
  File "<python-input-1>", line 2, in <module>
    config = WireguardConfig.from_wgconfig(fh)
  File "/usr/local/lib/python3.13/site-packages/wireguard_tools/wireguard_config.py", line 239, in from_wgconfig
    peer = WireguardPeer.from_wgconfig(key_value)
  File "/usr/local/lib/python3.13/site-packages/wireguard_tools/wireguard_config.py", line 132, in from_wgconfig
    return cls(**conf)
TypeError: WireguardPeer.__init__() missing 1 required positional argument: 'public_key'

This PR fixes it by only matching full lines for section headings.

[marksteward]

Technically we should be checking all lines for comments, and allowing inline comments after the sections too, but I'm not sure how rigorous we should be.