fix(chains): drop node URLs that embed Nova's provider keys (#72)

* fix(chains): drop node URLs that embed Nova's Infura keys

Nova's configs carry Nova's own Infura project keys inside node URLs, and
every sync copied them into ours: Ethereum had four keyed Infura nodes and
Base one, across 43 published files. Our Android build already fills
`{INFURA_API_KEY}` from our own secret; the keyed URLs used another
organisation's quota and would break for every user when Nova rotates them.

- sync_from_nova.py strips nodes whose URL embeds an Infura key, and drops a
  chain left with no node (only Ethereum - Goerli, a retired testnet, in the
  dev files); merge-chains.py applies the same filter
- the published chain files are rewritten with that filter; nothing else in
  them changes (each file round-trips byte for byte through json.dump)
- check_pezkuwi_integrity.py refuses a keyed Infura URL under chains/

* fix(chains): strip every keyed provider URL, and make the gate fail closed

The first pass matched only `infura.io/.../v3/<lowercase hex>`, so it missed
`https://...infura.io/v3/<key>`, upper-case keys and hosts, and Nova's
OnFinality `?apikey=` URLs (Moonriver, and the Hades testnet in v20/v21
preConfigured). preConfigured was copied from Nova without the filter, and the
integrity check passed if grep itself failed.

- one predicate, is_keyed(), in sync_from_nova.py: Infura /v3/ ids and
  apikey/api_key/key/token query values, case-insensitive; {PLACEHOLDER}
  values are allowed
- preConfigured details are filtered after the copy; a chain left with no
  node loses its details file and its index entry (Hades, v20/v21 only)
- rewritten files keep their own indent, so the diff is the data change only
- check 5 imports is_keyed() and checks every string in every JSON file
  under chains/; an unreadable file or an empty tree is an error
- check 3 reports a grep error instead of passing on it

chains/v21/chains.json

@@ -1676,25 +1676,9 @@
         "url": "https://1rpc.io/eth",
         "name": "One rpc node"
       },
-      {
-        "url": "wss://mainnet.infura.io/ws/v3/32a2be59297444c9bcb2b61bb700c6fe",
-        "name": "Infura node 5"
-      },
       {
         "url": "wss://mainnet.infura.io/ws/v3/{INFURA_API_KEY}",
         "name": "Infura node"
-      },
-      {
-        "url": "wss://mainnet.infura.io/ws/v3/1e69544301064ef19edb194a14fb75f3",
-        "name": "Infura node 2"
-      },
-      {
-        "url": "wss://mainnet.infura.io/ws/v3/9dddd77ac74043dc9a8dc48f82822c7d",
-        "name": "Infura node 4"
-      },
-      {
-        "url": "wss://mainnet.infura.io/ws/v3/82fd5b2925e341719f10b7ed4376a646",
-        "name": "Infura node 6"
       }
     ],
     "explorers": [