update nixpkgs

bitcoin: 30.2 -> 31.0
bitcoind: 30.2 -> 31.0
clboss: 0.15.1 -> 0.16.0
clightning: 25.12.1 -> 26.04.1
elementsd: 23.3.2 -> 23.3.3
lightning-loop: 0.31.5-beta -> 0.33.0-beta

lightning-loop 0.31.7+ blocks until lnd's chain notifier is ready
(lightninglabs/loop@bde49d7a), so the workaround sleep added in the
previous commit is no longer needed for lightning-loop. The
lightning-pool workaround stays — pool has no equivalent fix and
isn't actively maintained.

Note: nbxplorer test fails (presumed incompatibility with bitcoin 31).

flake.lock

@@ -44,11 +44,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1772822230,
-        "narHash": "sha256-yf3iYLGbGVlIthlQIk5/4/EQDZNNEmuqKZkQssMljuw=",
+        "lastModified": 1777673416,
+        "narHash": "sha256-5c2POKPOjU40Kh0MirOdScBLG0bu9TAuPYAtPRNZMBs=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "71caefce12ba78d84fe618cf61644dce01cf3a96",
+        "rev": "26ef669cffa904b6f6832ab57b77892a37c1a671",
         "type": "github"
       },
       "original": {
@@ -76,11 +76,11 @@
     },
     "nixpkgs-unstable": {
       "locked": {
-        "lastModified": 1772736753,
-        "narHash": "sha256-au/m3+EuBLoSzWUCb64a/MZq6QUtOV8oC0D9tY2scPQ=",
+        "lastModified": 1777826146,
+        "narHash": "sha256-wQ/iN5Zp5VIa3ebBibijPnLyKhor+xEbDy4d0goa9Zs=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "917fec990948658ef1ccd07cef2a1ef060786846",
+        "rev": "73c703c22422b8951895a960959dbbaca7296492",
         "type": "github"
       },
       "original": {