Add Palladium (PLM) coin

Palladium, PalladiumTestnet and PalladiumRegtest, with parameters from
palladiumcore (address prefixes, RPC ports, genesis hashes). The daemon
version/index requirements of the Bitcoin class are disabled, as Palladium Core
is based on Bitcoin Core 0.19.

Tests: chain params, address -> hashX, and mainnet block/transaction fixtures
taken from a synced node. The altcoin transaction test skips the address check
for witness outputs, as bech32 is not supported by Coin.address_to_hashX.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/lib/test_palladium.py

@@ -0,0 +1,41 @@
+# Tests of the Palladium coin classes (parameters from palladiumcore src/chainparams.cpp)
+
+import pytest
+
+from electrumx.lib import tx as lib_tx
+from electrumx.lib.coins import Coin, Palladium, PalladiumTestnet, PalladiumRegtest
+
+# (class, net, rpc port, P2PKH verbyte, P2SH verbyte, genesis hash)
+PARAMS = [
+    (Palladium, "mainnet", 2332, "37", "05",
+     "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"),
+    (PalladiumTestnet, "testnet", 12332, "7f", "73",
+     "000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943"),
+    (PalladiumRegtest, "regtest", 28443, "7f", "73",
+     "0f9188f13cb7b2c71f2a335e3a4fc328bf5beb436012afca590b1a11466e2206"),
+]
+
+
+@pytest.mark.parametrize("coin,net,rpc_port,p2pkh,p2sh,genesis", PARAMS)
+def test_chain_params(coin, net, rpc_port, p2pkh, p2sh, genesis):
+    assert coin.NAME == "Palladium"
+    assert coin.NET == net
+    assert coin.RPC_PORT == rpc_port
+    assert coin.P2PKH_VERBYTE == bytes.fromhex(p2pkh)
+    assert coin.P2SH_VERBYTES == (bytes.fromhex(p2sh),)
+    assert coin.GENESIS_HASH == genesis
+    assert coin.BASIC_HEADER_SIZE == 80
+    assert coin.DESERIALIZER is lib_tx.DeserializerSegWit
+
+
+@pytest.mark.parametrize("coin,net", [(c, n) for c, n, *_ in PARAMS])
+def test_lookup_coin_class(coin, net):
+    assert Coin.lookup_coin_class("Palladium", net) is coin
+    assert Coin.lookup_coin_class("palladium", net.upper()) is coin
+
+
+def test_daemon_requirements_disabled():
+    # Palladium Core (Bitcoin Core 0.19 based) has no getindexinfo/txospenderindex
+    for coin, *_ in PARAMS:
+        assert coin.MIN_REQUIRED_DAEMON_VERSION is None
+        assert not coin.REQUIRED_DAEMON_INDEXES