Add bidirectional DShot ESC telemetry

[halfmanbear]

Ports bidirectional DShot (GCR) telemetry from Betaflight, enabling RPM-based gyro filtering without a dedicated ESC telemetry UART.

After each DShot output frame the motor pin is switched to timer input capture mode via per-channel DMA to receive the ESC's GCR-encoded eRPM response. The decoded eRPM feeds the existing RPM filter infrastructure.

New settings:

• dshot_bidir_enabled: enable bidirectional DShot telemetry
• dshot_edt_enabled: enable Extended DShot Telemetry (temperature, voltage, current in addition to eRPM)

Changes:

• drivers/dshot.c/.h: GCR decode, EDT frame parsing, eRPM-to-RPM conversion, motor frequency LPF (ported from Betaflight, GPLv3)
• drivers/pwm_output.c: per-channel DMA direction switching between DShot output and GCR input capture on STM32 (StdPeriph/HAL) and AT32
• sensors/esc_sensor.c/.h: DShot bidir data path into ESC sensor framework (escSensorSetDshotData, escSensorIsActive)
• flight/rpm_filter.c: DShot telemetry as frequency source alongside serial ESC sensor path
• target/common_post.h: USE_RPM_FILTER enabled for any USE_DSHOT target
• fc/fc_init.c: call initDshotTelemetry() at startup; fix RPM filter init condition to accept DShot bidir as a valid source
• blackbox/blackbox.c: fix NULL dereference when escSensorGetData() returns NULL; fix uninitialized blackboxSlowState_t comparison
• telemetry/srxl.c: replace Betaflight-specific USE_DSHOT_TELEMETRY guards with INAV's USE_DSHOT/USE_ESC_SENSOR; use escSensorGetData()

Tested on SPEEDYBEEF405V4 (STM32F405, StdPeriph) with Bluejay ESC firmware. eRPM telemetry confirmed in blackbox;

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[github-actions]

Branch Targeting Suggestion

You've targeted the master branch with this PR. Please consider if a version branch might be more appropriate:

• maintenance-9.x - If your change is backward-compatible and won't create compatibility issues between INAV firmware and Configurator 9.x versions. This will allow your PR to be included in the next 9.x release.

• maintenance-10.x - If your change introduces compatibility requirements between firmware and configurator that would break 9.x compatibility. This is for PRs which will be included in INAV 10.x

If master is the correct target for this change, no action is needed.

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[Jetrell]

Have you had a chance to look at log data. To compare the latency improvement bdshot dynamic notch has over the matrix filter ? Or even over ESC telemetry RPM, to be sure it's working correctly.