refactor: Implement CodeRabbit suggestions for GHST telemetry tests

Added fake clock and TX buffer space as recommended by CodeRabbit review:
- Implemented fakeMicros static variable with testAdvanceMicros() helper
- Changed serialTxBytesFree() to return 64 instead of 0
- Added time advancement between processGhst() calls

However, tests still fail with zero values, indicating the GHST scheduler
requires additional conditions beyond basic time advancement. Possible causes:
- Frame type rotation logic
- Telemetry enable flags
- Inter-frame timing requirements
- Schedule index progression

Tests remain DISABLED with updated documentation explaining the current state
and what infrastructure has been implemented. Further investigation of GHST
frame scheduling system is needed to fully enable these tests.

Addresses CodeRabbitAI review #3376416184 MAJOR issue and 7 nitpicks.
All 38 test files still pass, 2 tests remain disabled with full documentation.

Author: nerdCopter

src/test/unit/telemetry_ghst_unittest.cc

@@ -92,6 +92,7 @@ extern "C" {
 extern "C" {
     uint8_t *ghstGetTelemetryBuf(void);     // Returns pointer to telemetryBuf
     uint8_t ghstGetTelemetryBufLen(void);   // Returns telemetryBufLen
+    void testAdvanceMicros(uint32_t delta); // Advance fake time for scheduler testing
 }
 
 #include "unittest_macros.h"
@@ -118,11 +119,10 @@ uint16_t    mAh Drawn
 // The firmware flow: processGhst() → writes to ghstFrame → ghstFinalize() → ghstRxWriteTelemetryData() → telemetryBuf
 // We access the firmware's telemetryBuf via accessor functions to validate the transmitted frame content.
 //
-// NOTE: DISABLED - processGhst() doesn't populate telemetryBuf with updated values on subsequent calls.
-// First call with zero values works, but second call after updating test variables still returns zeros.
-// Likely issue: processGhst() uses a schedule system and may only send frames at specific intervals,
-// or there's a state machine that's not being properly reset between calls.
-// Requires deeper investigation of GHST telemetry scheduling and state management.
+// NOTE: DISABLED - Further investigation needed. Added fake clock and TX buffer space per CodeRabbit suggestion,
+// but values still return 0. The GHST scheduler may require additional conditions beyond time advancement
+// (e.g., specific frame type rotation, telemetry enable flags, or inter-frame timing requirements).
+// Infrastructure is complete for future enabling once scheduler behavior is fully understood.
 TEST(TelemetryGhstTest, DISABLED_TestBattery)
 {
     uint16_t voltage;
@@ -139,6 +139,7 @@ TEST(TelemetryGhstTest, DISABLED_TestBattery)
     testmAhDrawn = 0;
 
     initGhstTelemetry();
+    testAdvanceMicros(50000); // Advance time to allow scheduler window to elapse
     processGhst();
 
     // Get telemetry buffer via accessor
@@ -164,6 +165,7 @@ TEST(TelemetryGhstTest, DISABLED_TestBattery)
     testAmperage = 2960; // = 29.60A = 29600mA - amperage is in 0.01A steps
     testmAhDrawn = 1234;
 
+    testAdvanceMicros(50000); // Advance time for next frame
     processGhst();
 
     // Get updated buffer (must call accessor again after processGhst)
@@ -184,7 +186,7 @@ TEST(TelemetryGhstTest, DISABLED_TestBattery)
 // Validates that firmware correctly sends per-cell voltage instead of pack voltage
 // when telemetryConfig()->report_cell_voltage is enabled.
 //
-// NOTE: DISABLED - Same issue as TestBattery. Telemetry buffer not being updated.
+// NOTE: DISABLED - Same as TestBattery. Requires further scheduler investigation.
 TEST(TelemetryGhstTest, DISABLED_TestBatteryCellVoltage)
 {
     uint16_t voltage;
@@ -205,6 +207,7 @@ TEST(TelemetryGhstTest, DISABLED_TestBatteryCellVoltage)
     telemetryConfigMutable()->report_cell_voltage = true;
 
     initGhstTelemetry();
+    testAdvanceMicros(50000); // Advance time to allow scheduler window to elapse
     processGhst();
 
     // Get telemetry buffer via accessor
@@ -243,12 +246,17 @@ gpsSolutionData_t gpsSol;
 
 void beeperConfirmationBeeps(uint8_t beepCount) {UNUSED(beepCount);}
 
-uint32_t micros(void) {return 0;}
+// Fake time for scheduler-driven telemetry
+static uint32_t fakeMicros = 0;
+void testAdvanceMicros(uint32_t delta) { fakeMicros += delta; }
+uint32_t micros(void) { return fakeMicros; }
+uint32_t microsISR(void) { return fakeMicros; }
 
 bool feature(uint32_t) {return true;}
 
 uint32_t serialRxBytesWaiting(const serialPort_t *) {return 0;}
-uint32_t serialTxBytesFree(const serialPort_t *) {return 0;}
+// Provide space so ghstRxWriteTelemetryData() can "send"
+uint32_t serialTxBytesFree(const serialPort_t *) { return 64; }
 uint8_t serialRead(serialPort_t *) {return 0;}
 void serialWrite(serialPort_t *, uint8_t) {}
 void serialWriteBuf(serialPort_t *, const uint8_t *, int) {}
@@ -310,9 +318,6 @@ bool isAmperageConfigured(void) { return true; }
 void setRssi(uint16_t, rssiSource_e){}
 rssiSource_e rssiSource;
 
-
-uint32_t microsISR(void) { return 0; };
-
 bool checkGhstTelemetryState(void) {
     return true;
 }