Bump the version to 0.5.1-rc.1 for the release candidate

Version only, and thrown away after the candidate reports. The candidate
exists to exercise the packaging matrix on a real tag: the publish path,
the AUR guard and the release-object creation, none of which a workflow
dispatch reaches. Every artifact this release ships comes from a build path
that did not exist at v0.5.0, which is why the candidate is worth its cost
here.

Cargo.lock

@@ -1144,7 +1144,7 @@ checksum = "9844ddc3a6e533d62bba727eb6c28b5d360921d5175e9ff0f1e621a5c590a4d5"
 
 [[package]]
 name = "fips"
-version = "0.5.1-dev"
+version = "0.5.1-rc.1"
 dependencies = [
  "arc-swap",
  "bech32 0.12.0",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "fips"
-version = "0.5.1-dev"
+version = "0.5.1-rc.1"
 edition = "2024"
 description = "A distributed, decentralized network routing protocol for mesh nodes connecting over arbitrary transports"
 license = "MIT"