Vendor the ASN.1 modules the codecs are verified against; untrack IDE churn

asn1/
Three tests assert exact bytes - CamEncodeGoldenTest, DenmAirReceiveTest and
SpatemUperCodecTest - and their expected values came from asn1tools compiled
against ETSI modules that existed only as an untracked working copy on one
machine. A golden-byte fixture nobody else can regenerate is a fixture nobody
can safely touch, so the modules are now in the repo.

Only the seven .asn files those tests need are copied, 576 KB of a 4.2 MB
checkout; the upstream Rust parser is not used by this project at all. Verified
sufficient in isolation: copied into an empty directory, all three specs compile
and reproduce the committed golden CAM bytes byte-identically.

Source is consider it GmbH's C-ITS-Parser (github.com/consider-it/C-ITS-Parser)
at f457426, MIT licensed - LICENSE is retained alongside as that requires. The
schemas themselves are ETSI's standard definitions; upstream's contribution is
assembling them into a compilable set. asn1/README.md records the provenance,
which module pairs with which message, and the rule that matters: never
regenerate a golden fixture from this project's own encoder, because sharing a
mistake between encoder and decoder is exactly the failure these files exist to
catch.

Doc references in the codecs and tests now point at asn1/ instead of the
untracked checkout, and C-ITS-Parser/ is gitignored so the working copy beside
the project is never picked up.

Untracked local state
- .idea/deploymentTargetSelector.xml rewrites itself on every deploy, so it has
  been showing as modified in essentially every commit. Along with
  deviceManager.xml, appInsightsSettings.xml and studiobot.xml it is per-machine
  state, not project configuration.
- obu-firmware/sdkconfig.old is ESP-IDF build output - it is the previous
  sdkconfig, rewritten on every build. sdkconfig.defaults remains tracked, since
  that is the configuration actually chosen.

All five stay on disk; only the tracking is removed. Also ignores
.claude/settings.local.json, which is per-machine, while leaving the skills
beside it committable as project knowledge.

.idea/appInsightsSettings.xml

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="AppInsightsSettings">
-    <option name="selectedTabId" value="Android vitals" />
-  </component>
-</project>

.idea/deploymentTargetSelector.xml

@@ -1,31 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="deploymentTargetSelector">
-    <selectionStates>
-      <SelectionState runConfigName="app">
-        <option name="selectionMode" value="DROPDOWN" />
-        <DropdownSelection timestamp="2026-08-05T15:07:39.343414600Z">
-          <Target type="DEFAULT_BOOT">
-            <handle>
-              <DeviceId pluginId="PhysicalDevice" identifier="serial=56211FDAP0015L" />
-            </handle>
-          </Target>
-        </DropdownSelection>
-        <DialogSelection>
-          <targets>
-            <Target type="DEFAULT_BOOT">
-              <handle>
-                <DeviceId pluginId="PhysicalDevice" identifier="serial=56211FDAP0015L" />
-              </handle>
-            </Target>
-            <Target type="DEFAULT_BOOT">
-              <handle>
-                <DeviceId pluginId="LocalEmulator" identifier="path=C:\Users\Ashin\.android\avd\Pixel_7_Pro.avd" />
-              </handle>
-            </Target>
-          </targets>
-        </DialogSelection>
-      </SelectionState>
-    </selectionStates>
-  </component>
-</project>

.idea/deviceManager.xml

@@ -1,13 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="DeviceTable">
-    <option name="columnSorters">
-      <list>
-        <ColumnSorterState>
-          <option name="column" value="Name" />
-          <option name="order" value="ASCENDING" />
-        </ColumnSorterState>
-      </list>
-    </option>
-  </component>
-</project>

.idea/studiobot.xml

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="StudioBotProjectSettings">
-    <option name="shareContext" value="OptedOut" />
-  </component>
-</project>