avcodec/vvcdec: thread, ensure the parse stage gets the highest priority

The parser stage is not parallelizable.
We need to schedule it as soon as possible to create later stages, which are more parallelizable

clips                                       | before | after | delta
--------------------------------------------|--------|-------|------
RitualDance_1920x1080_60_10_420_37_RA.266   | 342.7  | 365.3 |  6.59%
NovosobornayaSquare_1920x1080.bin           | 321.7  | 400   | 24.34%
Tango2_3840x2160_60_10_420_27_LD.266        |  82.3  |  91.7 | 11.42%
RitualDance_1920x1080_60_10_420_32_LD.266   | 323.7  | 319.3 | -1.36%
Chimera_8bit_1080P_1000_frames.vvc          | 364    | 411.3 | 12.99%
BQTerrace_1920x1080_60_10_420_22_RA.vvc     | 162.7  | 185.7 | 14.14%

libavcodec/vvc/thread.c

@@ -385,14 +385,15 @@ static int task_priority_higher(const AVTask *_a, const AVTask *_b)
     const VVCTask *a = (const VVCTask*)_a;
     const VVCTask *b = (const VVCTask*)_b;
 
-    CHECK(a->fc->decode_order, b->fc->decode_order);             //decode order
 
-    if (a->stage == VVC_TASK_STAGE_PARSE || b->stage == VVC_TASK_STAGE_PARSE) {
+    if (a->stage <= VVC_TASK_STAGE_PARSE || b->stage <= VVC_TASK_STAGE_PARSE) {
         CHECK(a->stage, b->stage);
+        CHECK(a->fc->decode_order, b->fc->decode_order);           //decode order
         CHECK(a->ry, b->ry);
         return a->rx < b->rx;
     }
 
+    CHECK(a->fc->decode_order, b->fc->decode_order);              //decode order
     CHECK(a->rx + a->ry + a->stage, b->rx + b->ry + b->stage);    //zigzag with type
     CHECK(a->rx + a->ry, b->rx + b->ry);                          //zigzag
     return a->ry < b->ry;