feat: Support 8 byte colors + non-linearity in hash (#466)

## Summary

- Support 8 byte color
- Add multiplication to fast hashing to achieve non-linearity
- Compensate slow down but deeper optimization (performance stays the
same)
- remove benchmake code and benchmark screenshots from repository



<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Moderate risk because `TileSignatureManager` now returns `null` when
the JNI library isn’t present, which can disable tiled diffing/session
replay in environments without `session_replay_c`. Also adjusts keyframe
selection logic for `OverlayTiles`, which could affect replay
fidelity/size.
> 
> **Overview**
> **Session replay tile hashing is now native-only.**
`TileSignatureManager` drops the Kotlin fallback/overloads and returns
`null` unless the `session_replay_c` JNI library is available.
> 
> **Tiled diff keyframe selection is adjusted.** `TileDiffManager`
changes `OverlayTiles` logic to treat `layers <= 0` as always-keyframe
and to prioritize periodic keyframes before falling back to
“whole-screen diff” detection.
> 
> **Benchmark and parity test code removed from the e2e app.** Deletes
the Compose `BenchmarkActivity`/executor/assets, removes its launcher
UI/manifest entry, removes the benchmark serialization dependency, and
deletes an Android instrumentation test that validated native/Kotlin
hash parity.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
9ee51d2. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: abelonogov-ld

e2e/android/app/build.gradle.kts

@@ -120,9 +120,6 @@ dependencies {
     implementation(platform(libs.androidx.compose.bom))
     implementation("androidx.compose.runtime:runtime")
 
-    // Serialization runtime (used by benchmark to encode replay events)
-    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.8.1")
-
     // Compose UI dependencies -- only for the compose flavor
     "composeImplementation"(libs.androidx.activity.compose)
     "composeImplementation"(libs.androidx.ui)

e2e/android/app/src/androidTest/java/com/example/androidobservability/TileHashParityInstrumentedTest.kt

@@ -15,12 +15,6 @@
         <activity
             android:name=".masking.ComposeWebActivity"
             android:exported="false" />
-        <activity
-            android:name=".benchmark.BenchmarkActivity"
-            android:exported="false"
-            android:label="Benchmark"
-            android:theme="@style/Theme.AndroidObservability" />
-
         <activity
             android:name=".MainActivity"
             android:exported="true"