Custom URI handler registration

[puddly]

This PR adds serialx.register_uri_handler, our new system of registering platforms. For example:

serialx.register_uri_handler(
    scheme="device://",
    unique_scheme="linux://",
    sync_cls=LinuxSerial,
    async_transport_cls=LinuxSerialTransport,
    list_serial_ports_func=linux_list_serial_ports,
    weight=3,
    strip_uri_scheme=True,
)

This will be used in the future to allow Home Assistant to register its own esphome-hass:// URI scheme to centralize ESPHome API connections within Core and to keep encryption keys out of integration config.

[codecov]

Codecov Report

❌ Patch coverage is 96.11650% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.86%. Comparing base (6109b77) to head (4ca2a79).
⚠️ Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
serialx/platforms/serial_esphome.py	66.66%	1 Missing ⚠️
serialx/platforms/serial_freebsd.py	75.00%	1 Missing ⚠️
serialx/platforms/serial_rfc2217/__init__.py	66.66%	1 Missing ⚠️
serialx/platforms/serial_socket.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #62      +/-   ##
==========================================
+ Coverage   89.67%   89.86%   +0.19%     
==========================================
  Files          19       19              
  Lines        2953     3010      +57     
==========================================
+ Hits         2648     2705      +57     
  Misses        305      305              

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