release: bump MCPP_VERSION source constant to 0.0.59

mcpp.toml was bumped but the binary reports MCPP_VERSION from
fingerprint.cppm; the release smoke-test (wrapper --version must match) caught
the mismatch. Bump the source constant too.

Author: Sunrisepeak

src/toolchain/fingerprint.cppm

@@ -18,7 +18,7 @@ import mcpp.toolchain.detect;
 
 export namespace mcpp::toolchain {
 
-inline constexpr std::string_view MCPP_VERSION = "0.0.58";
+inline constexpr std::string_view MCPP_VERSION = "0.0.59";
 
 struct FingerprintInputs {
     Toolchain                       toolchain;