Reduce key duplication by enabling hardware RNG (#8803)

* Reduce key duplication by enabling hardware RNG

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Apply suggestion from @Copilot

Use micros() for worst case random seed for nrf52

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Minor cleanup, remove dead code and clarify comment

* trunk

* Add useRadioEntropy bool, default false.

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>

src/mesh/HardwareRNG.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+
+namespace HardwareRNG
+{
+
+/**
+ * Fill the provided buffer with random bytes sourced from the most
+ * appropriate hardware-backed RNG available on the current platform.
+ *
+ * @param buffer Destination buffer for random bytes
+ * @param length Number of bytes to write
+ * @param useRadioEntropy If true, attempt to mix radio entropy into the output as well.
+ * @return true if the buffer was fully populated with entropy, false on failure
+ */
+bool fill(uint8_t *buffer, size_t length, bool useRadioEntropy = false);
+
+/**
+ * Populate a 32-bit seed value with hardware-backed randomness where possible.
+ *
+ * @param seedOut Destination for the generated seed value
+ * @return true if a seed was produced from a reliable entropy source
+ */
+bool seed(uint32_t &seedOut);
+
+} // namespace HardwareRNG