Merge #15163: Correct units for "-dbcache" and "-prune"

6f6514a080 Correct units for "-dbcache" and "-prune" (Hennadii Stepanov)

Pull request description:

  Actually, all `dbcache`-related values in the code are measured in MiB (not in megabytes, MB) or in bytes (e.g., `nTotalCache`).

  See: https://github.com/bitcoin/bitcoin/blob/master/src/txdb.h

  https://github.com/bitcoin/bitcoin/blob/ba8c8b22272ad40fe2de465d7e745532bab48d3b/src/init.cpp#L1405-L1424

  Also, "-prune" is fixed:
  1. The GUI values in GB are translated to the node values in MiB correctly.
  2. The maximum of the "prune" `QSpinBox` is not limited by default value of 99 (GB).

  Fix: #15106

Tree-SHA512: 151ec43b31b1074db8b345fedb1dcc10bde225899a5296bfc183f57e1553d13ac27db8db100226646769ad03c9fcab29d88763065a471757c6c41ac51108459d

test/functional/feature_pruning.py

@@ -320,7 +320,7 @@ class PruneTest(BitcoinTestFramework):
         if has_block(3):
             raise AssertionError("blk00003.dat is still there, should be pruned by now")
 
-        # stop node, start back up with auto-prune at 550MB, make sure still runs
+        # stop node, start back up with auto-prune at 550 MiB, make sure still runs
         self.stop_node(node_number)
         self.start_node(node_number, extra_args=["-prune=550"])