Document GDEY0213F52 fast-refresh mode as supported-but-omitted

The panel supports a faster full-color refresh (~11s vs 16s) via an
alternate init; it is not mono/partial. Noted at hasFastPartialUpdate so
consumers know the option exists for a future pass.

src/epd4c/GxEPD2_213c_GDEY0213F52.h

@@ -29,7 +29,12 @@ class GxEPD2_213c_GDEY0213F52 : public GxEPD2_EPD
     // command (R83H PTLW) adds a PTH_ENB bit vs. F51, so the F51 0x83 windowing is
     // not reused unverified; use the paged full-frame path (setPaged) meanwhile.
     static const bool hasPartialUpdate = false;
-    static const bool hasFastPartialUpdate = false; // F52 has a fast path (0xE0/0xE6/0xA5), not wired up yet
+    // NOTE: this panel also supports a faster refresh mode (~11s vs ~16s per datasheet)
+    // that Good Display's demo enables via an alternate init (0xE0=0x02, 0xE6=0x5A, 0xA5
+    // before power-on); the data write and 0x12 refresh are unchanged. It is still a
+    // full, flashing, full-color update - NOT a mono or partial/differential fast update.
+    // Support is intentionally omitted here; wiring it up means a dual full/fast init path.
+    static const bool hasFastPartialUpdate = false;
     static const uint16_t power_on_time = 200; // ms, e.g. 157485us
     static const uint16_t power_off_time = 100; // ms, e.g. 81338us
     static const uint16_t full_refresh_time = 16000; // ms, F52 spec'd 16 s full