Pack per-net bounding box state in NetCostHandler

[soheilshahrouz]

What changes in this PR:

• Committed state is packed per net. bb_coords_, bb_num_on_edges_ and net_cost_ are replaced by a single vtr::vector<ClusterNetId, t_net_bb_info>. avg_chan_util_ and net_cong_cost_ are replaced by net_cong_.
• Proposed state moves out of the per-net arrays. ts_bb_coord_new_, ts_bb_edge_new_, ts_avg_chan_util_new_, proposed_net_cost_, proposed_net_cong_cost_ and bb_update_status_ are replaced by a dense scratch array ts_net_info_, indexed by the net's position in ts_nets_to_update_.

[soheilshahrouz]

titan_other, SA placement time, 3 seeds

Circuit	master (s)	branch (s)	ratio
fir_cascade	148.05	149.06	1.0068
EKF-SLAM_Jacobians	133.61	131.73	0.9859
CHERI	117.08	114.91	0.9815
smithwaterman	90.97	91.40	1.0047
SURF_desc	99.86	98.82	0.9895
jacobi	94.70	93.50	0.9874
random	76.89	76.54	0.9954
CH_DFSIN	73.37	72.56	0.9889
JPEG	56.65	56.53	0.9978
carpat	67.58	67.21	0.9945
stap_steering	48.78	48.57	0.9957
MMM	44.92	45.01	1.0021
uoft_raytracer	68.11	67.52	0.9912
leon3mp	41.92	41.47	0.9893
MCML	69.35	69.28	0.9989
Reed_Solomon	29.24	28.87	0.9872
sudoku_check	15.85	15.87	1.0013
ucsb_152_tap_fir	9.67	9.67	0.9993
leon2	16.53	16.28	0.9851
wb_conmax	19.10	18.90	0.9895
radar20	10.48	10.44	0.9962
picosoc	10.31	10.18	0.9874
murax	0.89	0.89	1.0000
Geomean			0.9937

[soheilshahrouz]

titan_quick_qor, SA placement time, 3 seeds

Circuit	master (s)	branch (s)	ratio
neuron	121.36	120.98	0.9969
sparcT1_core	212.53	208.70	0.9820
stereo_vision	109.48	110.86	1.0126
cholesky_mc	209.99	211.21	1.0058
SLAM_spheric	331.60	328.54	0.9908
des90	385.99	384.04	0.9949
segmentation	663.81	664.20	1.0006
dart	521.97	519.24	0.9948
stap_qrd	1049.16	1041.26	0.9925
bitonic_mesh	851.63	850.95	0.9992
cholesky_bdti	616.46	617.77	1.0021
openCV	564.47	561.99	0.9956
minres	619.31	619.31	1.0000
sparcT2_core	1336.31	1316.69	0.9853
gsm_switch	1738.79	1731.65	0.9959
denoise	1687.96	1674.66	0.9921
mes_noc	3249.49	3212.81	0.9887
sparcT1_chip2	3835.62	3825.21	0.9973
LU_Network	3658.50	3646.59	0.9967
LU230	3068.93	3063.74	0.9983
directrf	7099.77	7171.14	1.0101
bitcoin_miner	6259.41	6297.65	1.0061
Geomean			0.9972