testnet update: rename testnet3 to testnet

Update all references to 'testnet3' to 'testnet' for consistency. This includes:
- Changing magic bytes in network messages
- Updating directory paths and configuration files
- Modifying documentation and test framework references
- Adjusting chain parameters and validation logic

test/functional/p2p_dos_header_tree.py

@@ -20,13 +20,13 @@ import os
 class RejectLowDifficultyHeadersTest(PalladiumTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
-        self.chain = 'testnet3'  # Use testnet chain because it has an early checkpoint
+        self.chain = 'testnet'
         self.num_nodes = 2
 
     def add_options(self, parser):
         parser.add_argument(
             '--datafile',
-            default='data/blockheader_testnet3.hex',
+            default='data/blockheader_testnet.hex',
             help='Test data file (default: %(default)s)',
         )
 
@@ -36,7 +36,7 @@ class RejectLowDifficultyHeadersTest(PalladiumTestFramework):
         with open(self.headers_file_path, encoding='utf-8') as headers_data:
             h_lines = [l.strip() for l in headers_data.readlines()]
 
-        # The headers data is taken from testnet3 for early blocks from genesis until the first checkpoint. There are
+        # The headers data is taken from testnet for early blocks from genesis until the first checkpoint. There are
         # two headers with valid POW at height 1 and 2, forking off from genesis. They are indicated by the FORK_PREFIX.
         FORK_PREFIX = 'fork:'
         self.headers = [l for l in h_lines if not l.startswith(FORK_PREFIX)]

test/functional/test_framework/mininode.py

@@ -90,7 +90,7 @@ MESSAGEMAP = {
 
 MAGIC_BYTES = {
     "mainnet": b"\xf9\xbe\xb4\xd9",   # mainnet
-    "testnet3": b"\x0b\x11\x09\x07",  # testnet3
+    "testnet": b"\x0c\x12\x0a\x08",  # testnet
     "regtest": b"\xfa\xbf\xb5\xda",   # regtest
 }
 

test/functional/test_framework/util.py

@@ -302,7 +302,7 @@ def initialize_datadir(dirname, n, chain):
     if not os.path.isdir(datadir):
         os.makedirs(datadir)
     # Translate chain name to config name
-    if chain == 'testnet3':
+    if chain == 'testnet':
         chain_name_conf_arg = 'testnet'
         chain_name_conf_section = 'test'
     else: