feat: add per output max-bpc config and ipc action

List current max-bpc values in outputs.

fix: remove 16 bpc and change default behaviour

feat(ipc): add max_bpc and format to output

fix: bpc on output config change

docs: add bpc to Outputs

feat: use atomic commits for connector properties

fix: drm `value_type` breaking change

fix: minor changes based on PR review

Rename bpc to max-bpc.

Add max-bpc output action.

refactor: add set_connector_properties

Fix niri-config parse test.

fix: bail when outside valid max bpc range

docs/wiki/Configuration:-Outputs.md

@@ -15,6 +15,7 @@ output "eDP-1" {
     variable-refresh-rate // on-demand=true
     focus-at-startup
     backdrop-color "#001100"
+    max-bpc 8
 
     hot-corners {
         // off
@@ -279,6 +280,23 @@ output "HDMI-A-1" {
 }
 ```
 
+### `max-bpc`
+
+<sup>Since: next release</sup>
+
+Set the maximum bits per channel (BPC) for this output.
+You *do not* need to set this option unless you hit bandwidth issues (can't set a monitor configuration that works on other compositor) or lower-than-expected color depth.
+Particularly, 10-bit color output may work even if max-bpc is 8.
+
+Valid values are `6`, `8`, `10`, `12`, `14`, `16`.
+
+```kdl
+// Set 8 max-bpc on HDMI-A-1 to lower the bandwidth.
+output "HDMI-A-1" {
+    max-bpc 8
+}
+```
+
 ### `hot-corners`
 
 <sup>Since: 25.11</sup>