bump minimum python to 3.9.2 and downgrade coincurve

This allows compatibility with python 3.14.0 which coincurve 21.0.0 did
not support.  The next coincurve release should restore compatibility.

Fixes: #8591

Changelog-changed: pyln-testing requires python>=3.9.2

Author: endothermicdev

contrib/pyln-proto/pyproject.toml

@@ -7,11 +7,11 @@ authors = [
 ]
 license = {text = "BSD-MIT"}
 readme = "README.md"
-requires-python = ">=3.9,<4.0"
+requires-python = ">=3.9.2,<4.0"
 dependencies = [
     "base58>=2.1.1",
     "bitstring>=4.3.0",
-    "coincurve==21.0.0",
+    "coincurve==20.0.0",
     "cryptography>=46",
     "PySocks>=1"
 ]

pyproject.toml

@@ -3,7 +3,7 @@ name = "cln-meta-project"
 version = "0.1.0"
 description = "Just a helper to get our python dependencies under control"
 authors = [{ name = "Christian Decker", email = "cdecker@blockstream.com" }]
-requires-python = ">=3.9,<4.0"
+requires-python = ">=3.9.2,<4.0"
 dependencies = [
   "Mako>=1.1.6",
   "websocket-client>=1.2.3",