feat: simple sensor panels with file-based data source (#7)

* add simulation mode for easier development

* improved sensor file watcher, poc cpu & mem usage

Trigger file read by rename event

* feat: system information sensor tool

Gather various sensor values with the sysinfo crate:
https://github.com/GuillaumeGomez/sysinfo
Values can be written to a sensor source file with the `--out` cmd line
option for the `asterctl` tool.

* ci: build sysinfo tool and include in build artifact

* feat: support integerDigits, decimalDigits sensor value format options

* docs: update documentation

Closes #6

.idea/runConfigurations/Run_sensor_panel_DEV.xml

@@ -0,0 +1,20 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Run sensor panel DEV" type="CargoCommandRunConfiguration" factoryName="Cargo Command">
+    <option name="buildProfileId" value="dev" />
+    <option name="command" value="run --package aoostar-rs --bin asterctl -- -c monitor.json --save --simulate" />
+    <option name="workingDirectory" value="file://$PROJECT_DIR$" />
+    <envs />
+    <option name="emulateTerminal" value="true" />
+    <option name="channel" value="DEFAULT" />
+    <option name="requiredFeatures" value="true" />
+    <option name="allFeatures" value="false" />
+    <option name="withSudo" value="false" />
+    <option name="buildTarget" value="REMOTE" />
+    <option name="backtrace" value="SHORT" />
+    <option name="isRedirectInput" value="false" />
+    <option name="redirectInputPath" value="" />
+    <method v="2">
+      <option name="CARGO.BUILD_TASK_PROVIDER" enabled="true" />
+    </method>
+  </configuration>
+</component>