perf(common): reduce the average recusrion depth in _flatten_collections

[kszucs]

_flatten_collections() is called with a sequence node.__args__ and instead of checking for a sequence then recursing into another call, now it directly iterates over the input sparing a constant function call for each node in each traversal.

---------------------------------------------------------------------------- benchmark 'test_bfs': 2 tests -----------------------------------------------------------------------------
Name (time in ms)              Min               Max              Mean            StdDev            Median               IQR            Outliers       OPS            Rounds  Iterations
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
test_bfs (0673_5041894)     2.2382 (1.20)     2.9203 (1.24)     2.3931 (1.23)     0.1005 (1.34)     2.3806 (1.24)     0.1482 (2.74)         48;3  417.8750 (0.81)        178           1
test_bfs (NOW)              1.8689 (1.0)      2.3535 (1.0)      1.9434 (1.0)      0.0752 (1.0)      1.9226 (1.0)      0.0541 (1.0)         23;20  514.5500 (1.0)         208           1
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------- benchmark 'test_dfs': 2 tests -----------------------------------------------------------------------------
Name (time in ms)              Min               Max              Mean            StdDev            Median               IQR            Outliers       OPS            Rounds  Iterations
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
test_dfs (0673_5041894)     2.2766 (1.19)     2.8229 (1.25)     2.4995 (1.23)     0.1268 (1.68)     2.4992 (1.22)     0.1543 (1.37)         12;1  400.0872 (0.82)         39           1
test_dfs (NOW)              1.9076 (1.0)      2.2635 (1.0)      2.0371 (1.0)      0.0754 (1.0)      2.0467 (1.0)      0.1129 (1.0)          56;2  490.9033 (1.0)         189           1
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------- benchmark 'test_replace_mapping': 2 tests ------------------------------------------------------------------------------
Name (time in ms)                          Min                Max               Mean            StdDev            Median               IQR            Outliers       OPS            Rounds  Iterations
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
test_replace_mapping (0673_5041894)     9.0726 (1.06)     30.7215 (1.13)     10.2926 (1.09)     3.2098 (1.0)      9.7669 (1.12)     0.5696 (3.24)          2;3   97.1575 (0.92)         77           1
test_replace_mapping (NOW)              8.5212 (1.0)      27.3008 (1.0)       9.4436 (1.0)      3.2393 (1.01)     8.7318 (1.0)      0.1755 (1.0)          3;13  105.8916 (1.0)          83           1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

------------------------------------------------------------------------------ benchmark 'test_replace_pattern': 2 tests ------------------------------------------------------------------------------
Name (time in ms)                           Min                Max               Mean            StdDev             Median               IQR            Outliers      OPS            Rounds  Iterations
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
test_replace_pattern (0673_5041894)     12.6172 (1.03)     32.6150 (1.02)     14.1622 (1.05)     3.2321 (1.0)      13.5553 (1.05)     0.7407 (1.0)           3;3  70.6105 (0.95)         61           1
test_replace_pattern (NOW)              12.2255 (1.0)      32.0460 (1.0)      13.4309 (1.0)      3.4930 (1.08)     12.9361 (1.0)      0.7598 (1.03)          2;2  74.4554 (1.0)          59           1