gh-106078: Prepare to isolate decimal module

[CharlieZhao95]

The DecCondMap contains a potentially global variable(ex, a subclass of DecimalException). We should also move signal_map and cond_map to module state.

• Move signal_map and cond_map to global state
• Initialize array of DecCondMap using heap memory (Prepare to isolate module)

• Issue: Isolate the _decimal extension module #106078

[CharlieZhao95]

cc: @erlend-aasland @kumaraditya303

[kumaraditya303]

root@codespaces-62bef3 /w/cpython (decimal/move_condmap)# ./python -m test -R 3:3 test_decimal
0:00:00 load avg: 37.18 Run tests sequentially
0:00:00 load avg: 37.18 [1/1] test_decimal
beginning 6 repetitions
123456
......

== Tests result: SUCCESS ==

1 test OK.

Total duration: 26.0 sec
Tests result: SUCCESS