base: Add e1000d interrupt throttling rate (ITR) coalescing (P53)

Re-implements work that was lost due to ephemeral source/ subdirectory.
ITR dynamically adjusts interrupt coalescing based on packet rate.

- Add ITR register (0xC4) and set_itr() to device.rs
- Add itr.rs tracker with hysteresis-based rate adaptation
- Wire tracker into IRQ handler in main.rs
- Document in AGENTS.md: source/ is ALWAYS rewritten

recipes/core/base/P53-e1000d-itr-coalescing.patch

@@ -0,0 +1 @@
+../../../local/patches/base/P53-e1000d-itr-coalescing.patch

recipes/core/base/recipe.toml

@@ -105,6 +105,8 @@ patches = [
     "P51-logd-rotation.patch",
     # P52: Add ACPI C-state discovery and thermal-based C-state policy
     "P52-acpid-cstates.patch",
+    # P53: Add e1000d interrupt throttling rate (ITR) coalescing
+    "P53-e1000d-itr-coalescing.patch",
 ]
 
 [package]