fix(ci): repair all 3 QEMU workflow job failures

1. Fuzz Tests: add esp_timer_create_args_t, esp_timer_create(),
   esp_timer_start_periodic(), esp_timer_delete() stubs to
   esp_stubs.h — csi_collector.c uses these for channel hop timer.

2. QEMU Build: add libgcrypt20-dev to apt dependencies —
   Espressif QEMU's esp32_flash_enc.c includes <gcrypt.h>.
   Bump cache key v4→v5 to force rebuild with new dep.

3. NVS Matrix: switch to subprocess-first invocation of
   nvs_partition_gen to avoid 'str' has no attribute 'size' error
   from esp_idf_nvs_partition_gen API change. Falls back to
   direct import with both int and hex size args.

Co-Authored-By: claude-flow <ruv@ruv.net>

.github/workflows/firmware-qemu.yml

@@ -38,7 +38,7 @@ jobs:
         with:
           path: /opt/qemu-esp32
           # Include date component so cache refreshes monthly when branch updates
-          key: qemu-esp32s3-${{ env.QEMU_BRANCH }}-v4
+          key: qemu-esp32s3-${{ env.QEMU_BRANCH }}-v5
           restore-keys: |
             qemu-esp32s3-${{ env.QEMU_BRANCH }}-
 
@@ -49,6 +49,7 @@ jobs:
           sudo apt-get install -y \
             git build-essential ninja-build pkg-config \
             libglib2.0-dev libpixman-1-dev libslirp-dev \
+            libgcrypt20-dev \
             python3 python3-venv
 
       - name: Clone and build Espressif QEMU