refactor(task,render): RenderTask family over a new oakrender ticket C ABI

- oakrender: new ticket family (render_frame/render_audio with finished
  callback, result frame/samples access, cancel/wait), project copier
  C API, cache get_invalidated_ranges, manager set_aggressive_gc
- oaknode: node_copy_inputs, set_value_hint_track, viewer params
  setters, video frame cache borrowed outlet, project copy_settings
- oakcodec: encoder desired pixel format, export format extension,
  encoding generate_matrix, custom range in encoding params POD
- oaktask: RenderTask orchestrates oakrender tickets (no Qt threads/
  watchers), PreCacheTask and ExportTask rewritten over the oaknode/
  oakrender/oakcodec C ABIs; frames cross from oakrender to oakcodec
  handles by pixel copy (different control blocks)
- the two-step texture/download render path collapses into single-step
  (tickets always yield frames); subtitle sidecar kept
- tests: 105 in build-oaktask (export/precache factory paths,
  construction, conform end-to-end); regressions all green

include/codec/encoder.h

@@ -116,6 +116,14 @@ typedef struct oakcodec_encoding_params {
 
 	int export_length_num; /**< Export length in seconds (rational). */
 	int export_length_den;
+
+	/** Custom export range (seconds, rational pairs); used when
+	 * has_custom_range != 0. */
+	int has_custom_range;
+	int64_t custom_range_in_num;
+	int64_t custom_range_in_den;
+	int64_t custom_range_out_num;
+	int64_t custom_range_out_den;
 } oakcodec_encoding_params;
 
 /**
@@ -185,6 +193,29 @@ OAKCODEC_API int oakcodec_encoder_flush(OakEncoder encoder);
  */
 OAKCODEC_API int oakcodec_encoder_last_error(OakEncoder encoder, char *buf, int buf_size);
 
+/**
+ * @brief The pixel format the encoder wants frames in
+ *        (Encoder::get_desired_pixel_format()), as int; -1 when
+ *        unknown/invalid encoder.
+ */
+OAKCODEC_API int oakcodec_encoder_get_desired_pixel_format(OakEncoder encoder);
+
+/**
+ * @brief File extension for an export format
+ *        (ExportFormat::get_extension()), two-stage string getter.
+ */
+OAKCODEC_API int oakcodec_export_format_get_extension(int format, char *buf,
+									 int buf_size);
+
+/**
+ * @brief Scaling matrix for a scaling method
+ *        (EncodingParams::generate_matrix()), row-major 4x4 into
+ *        out_matrix[16].
+ */
+OAKCODEC_API int oakcodec_encoding_generate_matrix(int method, int src_width,
+								  int src_height, int dst_width,
+								  int dst_height, double *out_matrix);
+
 #ifdef __cplusplus
 }
 #endif