call Gc.compact periodically

[deepthiskumar]

Calling Gc.compact periodically to free the memory held
Below is the result of calling Gc.compact from utop (it reduced heap words from ~13GB to ~5GB)

# Gc.stat ();;
- : Gc.stat =
{Gc.minor_words = 2294978993287.; promoted_words = 15080030917.;
 major_words = 20958098793.; minor_collections = 8761351;
 major_collections = 216; heap_words = 1715582464; heap_chunks = 59;
 live_words = 526574411; live_blocks = 142165064; free_words = 1188950267;
 free_blocks = 2149630; largest_free = 1546702; fragments = 57786;
 compactions = 0; top_heap_words = 1715582464; stack_size = -17469354802087}
# Gc.compact ();;
- : unit = ()
# Gc.stat ();;
- : Gc.stat =
{Gc.minor_words = 2302521471864.; promoted_words = 15123686288.;
 major_words = 21010814070.; minor_collections = 8790126;
 major_collections = 219; heap_words = 734692864; heap_chunks = 4;
 live_words = 394400770; live_blocks = 112766591; free_words = 340292094;
 free_blocks = 3; largest_free = 169203712; fragments = 0; compactions = 1;
 top_heap_words = 1715582464; stack_size = -17469354802221}

1. Periodically calling Gc.compact in the daemon for proof-level FULL

2. Added two environment variables MINA_COMPACTION_MS and MINA_COMPACTION_INTERVAL_MS to set expected compaction time (default: 6000 ms) and time between calling Gc.compact (default: slot_duration * 2) respectively.

Ran the daemon with the default values for ~6 hours. It did reduced the heap words, but the memory usage still grew linearly

Closes #7542

[mrmr1993]

Very nice!