refactor: replace custom runtime with Go stdlib runtime/debug

[paganotoni]

Summary

This PR modernizes the buffalo runtime package by replacing the custom build-time ldflags injection with Go's standard library runtime/debug package.

Changes

Breaking Changes

• runtime.Version now defaults to 'dev' instead of hardcoded 'v1.1.0'
• BuildInfo.Time now uses VCS commit time (vcs.time) instead of build time
• The entire runtime package is now deprecated and will be removed in v2

Implementation Details

• Removed underscore import of runtime package from buffalo.go
• runtime.Build() now internally uses debug.ReadBuildInfo()
• All public APIs marked as deprecated with migration instructions
• Deleted runtime/version.go (content merged into build.go)
• Added CHANGELOG.md with comprehensive migration guide

Backward Compatibility

✅ The runtime package API remains fully backward compatible:

• runtime.Build() works the same way
• runtime.Version is still accessible
• runtime.SetBuild() still exists (though now a no-op after first Build() call)

Migration Path

Users can modernize their code to use runtime/debug directly:

// Old way (still works, but deprecated)
import "github.com/gobuffalo/buffalo/runtime"
info := runtime.Build()

// New recommended way
import "runtime/debug"
info, ok := debug.ReadBuildInfo()
if ok {
    version := info.Main.Version
    // Access VCS info via info.Settings
    for _, s := range info.Settings {
        switch s.Key {
        case "vcs.revision":
            // commit hash
        case "vcs.time":
            // commit timestamp
        case "vcs.modified":
            // "true" if working tree had uncommitted changes
        }
    }
}

Testing

All existing tests pass:

• go build ./... - successful
• go test ./... -short - all packages pass

Requirements

• Go 1.18+ (for VCS information embedding)
• Binary must be built with module support

Related

This change eliminates the vendoring workaround that required the blank import in buffalo.go, modernizing the codebase to use standard Go practices.