Use AS_COMPACT collocation for gcp placement groups

[r4victor]

Closes #2586

Tested with n1-highmem-2, a3-highgpu-8g, a3-megagpu-8g. Better results for a3-highgpu-8g and a3-megagpu-8g. n1-highmem-2 works and is as slow as before, so no noticeable downgrade.

NCCL tests on a3-highgpu-8g:

#                                                              out-of-place                       in-place          
#       size         count      type   redop    root     time   algbw   busbw #wrong     time   algbw   busbw #wrong
#        (B)    (elements)                               (us)  (GB/s)  (GB/s)            (us)  (GB/s)  (GB/s)       
     1048576         16384     float    none      -1    627.4    1.67    1.57      0    614.6    1.71    1.60      0
     2097152         32768     float    none      -1    657.1    3.19    2.99      0    641.2    3.27    3.07      0
     4194304         65536     float    none      -1    669.6    6.26    5.87      0    688.5    6.09    5.71      0
     8388608        131072     float    none      -1    811.5   10.34    9.69      0    729.4   11.50   10.78      0
    16777216        262144     float    none      -1    964.5   17.39   16.31      0    945.5   17.74   16.64      0
    33554432        524288     float    none      -1   1100.9   30.48   28.57      0   1080.8   31.05   29.11      0
    67108864       1048576     float    none      -1   1375.0   48.81   45.76      0   1345.9   49.86   46.75      0
   134217728       2097152     float    none      -1   2418.1   55.51   52.04      0   2434.0   55.14   51.70      0
   268435456       4194304     float    none      -1   4871.5   55.10   51.66      0   4857.8   55.26   51.81      0
   536870912       8388608     float    none      -1   9944.5   53.99   50.61      0   9952.2   53.95   50.57      0
  1073741824      16777216     float    none      -1    19626   54.71   51.29      0    19534   54.97   51.53      0
  2147483648      33554432     float    none      -1    37732   56.91   53.36      0    37323   57.54   53.94      0
  4294967296      67108864     float    none      -1    73500   58.43   54.78      0    73449   58.48   54.82      0
  8589934592     134217728     float    none      -1   147172   58.37   54.72      0   146112   58.79   55.12      0
# Out of bounds values : 0 OK
# Avg bus bandwidth    : 34.3695 
#

NCCL tests on a3-megagpu-8g:

#
#                                                              out-of-place                       in-place          
#       size         count      type   redop    root     time   algbw   busbw #wrong     time   algbw   busbw #wrong
#        (B)    (elements)                               (us)  (GB/s)  (GB/s)            (us)  (GB/s)  (GB/s)       
     8388608        131072     float    none      -1    147.4   56.91   53.35    N/A    144.8   57.94   54.32    N/A
    16777216        262144     float    none      -1    177.6   94.45   88.55    N/A    174.4   96.23   90.21    N/A
    33554432        524288     float    none      -1    258.8  129.68  121.57    N/A    258.0  130.04  121.91    N/A
    67108864       1048576     float    none      -1    433.1  154.96  145.27    N/A    429.1  156.40  146.63    N/A
   134217728       2097152     float    none      -1    794.8  168.87  158.32    N/A    787.5  170.43  159.78    N/A
   268435456       4194304     float    none      -1   1508.3  177.97  166.85    N/A   1497.0  179.31  168.10    N/A
   536870912       8388608     float    none      -1   2852.5  188.21  176.45    N/A   2837.8  189.19  177.36    N/A
  1073741824      16777216     float    none      -1   5502.5  195.14  182.94    N/A   5496.2  195.36  183.15    N/A
  2147483648      33554432     float    none      -1    10814  198.59  186.18    N/A    10800  198.85  186.42    N/A
  4294967296      67108864     float    none      -1    21433  200.39  187.86    N/A    21410  200.61  188.07    N/A
  8589934592     134217728     float    none      -1    42639  201.46  188.87    N/A    42622  201.54  188.94    N/A
# Out of bounds values : 0 OK
# Avg bus bandwidth    : 150.96 
#