[jianj-g]

Fix existing segmentation and quantizer state synchronization issues in
cyclic refresh (CYCLIC_REFRESH_AQ / aq-mode=3) and adapt its core
parameters, 1-pass CBR rate control, and variance-based partitioning to
AV2:

• Remove unused last_coded_q_map allocation and fix the out-of-bounds
  write on keyframes in av2_cyclic_refresh_setup().
• Adapt compute_deltaq(), qp_thresh, qp_max_thresh, and thresh_dist_sb
  to AV2's logarithmic qindex scale and bit-depth offset
  (MAXQ_FOR_GIVEN_BIT_DEPTH), and scale rate/distortion thresholds in
  candidate_refresh_aq() for BLOCK_128X128 and BLOCK_256X256 superblocks.
• Update segment_id on skip_txfm, propagate segment_id to
  cur_frame->seg_map, enc_seg.map, and cr->map, and re-initialize plane
  quantizers inside av2_cyclic_refresh_update_segment().
• Add av2_cyclic_reset_segment_skip() in encode_b() when skip_txfm is
  finalized after encode_superblock(), and accumulate per-thread cyclic
  refresh counters (actual_num_seg1_blocks, actual_num_seg2_blocks,
  cnt_zeromv) across worker threads.
• Enable CYCLIC_REFRESH_AQ in encode_with_recode_loop(), dynamically
  adapt cyclic refresh percentage and delta-q in
  av2_cyclic_refresh_postencode(), and integrate cyclic refresh with
  1-pass CBR rate control in ratectrl.c.
• Use segment-adjusted qindex in av2_choose_var_based_partitioning()
  when cyclic refresh segmentation is enabled so boosted superblocks are
  not over-merged by high-Q threshold relaxations.
• Add unit tests in aq_segment_test.cc, rtc_test.cc, and
  rtc_datarate_test.cc covering aq-mode=3 across RTC speeds, superblock
  sizes (64x64, 128x128, 256x256, dynamic), screen content, row-MT, and
  CBR rate targeting.

5.6% bdrate gain / 8.8% speed up on RTC test set compared with aq mode 0
on speed 6.