Add intervalometer filter for automatic exposure control

Implements YASS-inspired automatic exposure control for IDS uEye cameras.
The intervalometer filter analyzes video brightness in real-time and
smoothly ramps camera exposure and gain settings during changing light
conditions - ideal for sunset/sunrise time-lapse photography.

Key features:
- Automatic exposure ramping (0.85-1.24ms configurable range)
- Automatic gain control (0-52 configurable range)
- Real-time brightness analysis (GRAY8, GRAY16, RGB, BGR, BGRA)
- YASS-inspired ramping algorithm (exposure priority, then gain)
- Configurable ramp rates (VSlow/Slow/Medium/Fast/VFast)
- Exposure compensation (±4 stops)
- CSV logging of exposure parameters
- Direct GObject property control (no message bus overhead)

Technical implementation:
- GstBaseTransform filter for in-place processing
- Discovers upstream camera element by name
- Controls camera via g_object_set() for synchronous updates
- Frame-by-frame brightness calculation with format support

Files added:
- gst/intervalometer/gstintervalometer.c: Main implementation (734 lines)
- gst/intervalometer/gstintervalometer.h: Header with structure definitions
- gst/intervalometer/CMakeLists.txt: Build configuration
- gst/intervalometer/README.md: Comprehensive documentation

Files modified:
- gst/CMakeLists.txt: Added intervalometer subdirectory
- build.ps1: Added intervalometer to build and deployment pipeline

Usage example:
  gst-launch-1.0 idsueyesrc name=cam ! \\
    intervalometer enabled=true camera-element=cam \\
      exposure-min=0.85 exposure-max=1.24 \\
      gain-min=0 gain-max=52 ramp-rate=medium ! \\
    autovideosink

Inspired by YASS (Yet Another Sunset Script) for CHDK cameras by
waterwingz, based on work by Fbonomi and soulf2.

gst/intervalometer/gstintervalometer.h

@@ -0,0 +1,104 @@
+/* GStreamer
+ * Copyright (C) 2024 FIXME <fixme@example.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#ifndef __GST_INTERVALOMETER_H__
+#define __GST_INTERVALOMETER_H__
+
+#include <stdio.h>
+#include <gst/base/gstbasetransform.h>
+#include <gst/video/video.h>
+
+G_BEGIN_DECLS
+
+#define GST_TYPE_INTERVALOMETER \
+  (gst_intervalometer_get_type())
+#define GST_INTERVALOMETER(obj) \
+  (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_INTERVALOMETER,GstIntervalometer))
+#define GST_INTERVALOMETER_CLASS(klass) \
+  (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_INTERVALOMETER,GstIntervalometerClass))
+#define GST_IS_INTERVALOMETER(obj) \
+  (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_INTERVALOMETER))
+#define GST_IS_INTERVALOMETER_CLASS(klass) \
+  (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_INTERVALOMETER))
+
+typedef struct _GstIntervalometer GstIntervalometer;
+typedef struct _GstIntervalometerClass GstIntervalometerClass;
+
+typedef enum {
+  RAMP_RATE_VSLOW = 0,
+  RAMP_RATE_SLOW,
+  RAMP_RATE_MEDIUM,
+  RAMP_RATE_FAST,
+  RAMP_RATE_VFAST
+} GstIntervalometerRampRate;
+
+/**
+ * GstIntervalometer:
+ * @element: the parent element.
+ *
+ * Auto-exposure controller for IDS uEye cameras.
+ * Inspired by YASS (Yet Another Sunset Script) for CHDK cameras.
+ */
+struct _GstIntervalometer
+{
+  GstBaseTransform element;
+
+  /* Properties */
+  gboolean enabled;
+  gdouble target_brightness;     /* Target average brightness (0-255) */
+  gdouble compensation;          /* Exposure compensation in stops */
+  gdouble exposure_min;          /* Minimum exposure in ms */
+  gdouble exposure_max;          /* Maximum exposure in ms */
+  gint gain_min;                 /* Minimum gain (0-100) */
+  gint gain_max;                 /* Maximum gain (0-100) */
+  GstIntervalometerRampRate ramp_rate;
+  gchar *log_file;               /* CSV log file path */
+  gchar *camera_element_name;    /* Name of upstream idsueyesrc element */
+
+  /* Internal state */
+  GstElement *camera_src;        /* Reference to upstream camera element */
+  gdouble current_exposure;      /* Current exposure setting */
+  gint current_gain;             /* Current gain setting */
+  gdouble target_exposure;       /* Target exposure for ramping */
+  gint target_gain;              /* Target gain for ramping */
+  
+  guint64 frame_count;           /* Number of frames processed */
+  GstClockTime start_time;       /* Time when processing started */
+  
+  FILE *log_fp;                  /* Log file handle */
+  gboolean log_header_written;   /* Whether CSV header has been written */
+  
+  /* Video info */
+  GstVideoInfo video_info;
+  gboolean video_info_valid;
+  
+  /* Ramping parameters */
+  gdouble ramp_step;             /* Current ramping step size */
+};
+
+struct _GstIntervalometerClass
+{
+  GstBaseTransformClass parent_class;
+};
+
+GType gst_intervalometer_get_type(void);
+
+G_END_DECLS
+
+#endif /* __GST_INTERVALOMETER_H__ */