Leave src/platform out of the build filter by default (#10726)

* Leave src/platform out of the build filter by default, and only add back what each build needs.

* typo fix

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

variants/native/portduino.ini

@@ -6,13 +6,10 @@ platform =
 framework = arduino
 
 build_src_filter = 
-  ${env.build_src_filter} 
-  -<platform/esp32/> 
+  ${env.build_src_filter}
+  -<platform/>
+  +<platform/portduino>
   -<nimble/> 
-  -<platform/nrf52/>
-  -<platform/nrf54l15/>
-  -<platform/stm32wl/>
-  -<platform/rp2xx0>
   -<mesh/wifi/>
   -<mesh/http/>
   +<mesh/raspihttp/>