Prepare C# Payjoin 0.25.0-preview.1 for NuGet

Bump the package from 0.24.0-preview.1 for the release wrapping
payjoin-1.0.0. The package version tracks the payjoin-ffi crate
version with a -preview.N suffix while the C# API stabilizes, so
the crate bump to 0.25.0 moves the base version and restarts the
preview counter.

Author: spacebear21

payjoin-ffi/csharp/Payjoin.csproj

@@ -7,7 +7,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPackable>true</IsPackable>
     <PackageId>Payjoin</PackageId>
-    <Version>0.24.0-preview.1</Version>
+    <Version>0.25.0-preview.1</Version>
     <Title>Payjoin</Title>
     <Authors>Payjoin Dev Kit Contributors</Authors>
     <Description>C# bindings for payjoin-ffi, generated from rust-payjoin via UniFFI.</Description>