Use modern config for maturin. (#16394)

This allows maturin >= 0.15 to build the properly named
shared library object.

For now the old configuration is also kept to allow for
older maturin installs to be used.

rust/Cargo.toml

@@ -15,6 +15,8 @@ name = "synapse"
 # tests/benchmarks.
 crate-type = ["lib", "cdylib"]
 
+# This is deprecated, see tool.maturin in pyproject.toml.
+# It is left here for compatibilty with maturin < 0.15.
 [package.metadata.maturin]
 # This is where we tell maturin where to place the built library.
 name = "synapse.synapse_rust"