Merge bitcoin/bitcoin#31046: init: Some small chainstate load improvements

31cc5006c3 init: Return fatal failure on snapshot validation failure (Martin Zumsande)
8f1246e833 init: Improve chainstate init db error messages (TheCharlatan)
cd093049dd init: Remove incorrect comment about shutdown condition (MarcoFalke)
635e9f85d7 init: Remove misleading log line when user chooses not to retry (TheCharlatan)
720ce880a3 init: Improve comment describing chainstate load retry behaviour (Martin Zumsande)
baea842ff1 init: Remove unneeded argument for mempool_opts checks (stickies-v)

Pull request description:

  These are mostly followups from #30968, making the code, log lines, error messages, and comments more consistent.

  The last commit is an attempt at improving the error reporting when loading the chainstate. It aims to more cleanly distinguish between errors arising from a specific database, and errors where the culprit may be less clear.

ACKs for top commit:
  achow101:
    ACK 31cc5006c3
  mzumsande:
    Code Review / lightly tested ACK 31cc5006c3
  BrandonOdiwuor:
    Code Review ACK 31cc5006c3.
  stickies-v:
    ACK 31cc5006c3

Tree-SHA512: 59fba4845ee45a3d91bf55807ae6b1c81458463b96bf664c8b1badfac503f6b01efd52a915fc399294e68a3f69985362a5a10a3844fa23f7707145ebe9ad349b

test/functional/feature_init.py

@@ -100,13 +100,13 @@ class InitTest(BitcoinTestFramework):
 
         files_to_delete = {
             'blocks/index/*.ldb': 'Error opening block database.',
-            'chainstate/*.ldb': 'Error opening block database.',
+            'chainstate/*.ldb': 'Error opening coins database.',
             'blocks/blk*.dat': 'Error loading block database.',
         }
 
         files_to_perturb = {
             'blocks/index/*.ldb': 'Error loading block database.',
-            'chainstate/*.ldb': 'Error opening block database.',
+            'chainstate/*.ldb': 'Error opening coins database.',
             'blocks/blk*.dat': 'Corrupted block database detected.',
         }