Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/golang-migrate/migrate/v4/util.go

@@ -0,0 +1,63 @@
+package migrate
+
+import (
+	"fmt"
+	nurl "net/url"
+	"strings"
+)
+
+// MultiError holds multiple errors.
+//
+// Deprecated: Use stdlib's [errors.Join] et al. instead
+// This will be removed in the v5 release.
+type MultiError struct {
+	Errs []error
+}
+
+// NewMultiError returns an error type holding multiple errors.
+//
+// Deprecated: Use stdlib's [errors.Join] et al. instead
+// This will be removed in the v5 release.
+func NewMultiError(errs ...error) MultiError {
+	compactErrs := make([]error, 0)
+	for _, e := range errs {
+		if e != nil {
+			compactErrs = append(compactErrs, e)
+		}
+	}
+	return MultiError{compactErrs}
+}
+
+// Error implements error. Multiple errors are concatenated with 'and's.
+func (m MultiError) Error() string {
+	var strs = make([]string, 0)
+	for _, e := range m.Errs {
+		if len(e.Error()) > 0 {
+			strs = append(strs, e.Error())
+		}
+	}
+	return strings.Join(strs, " and ")
+}
+
+// suint safely converts int to uint
+// see https://goo.gl/wEcqof
+// see https://goo.gl/pai7Dr
+func suint(n int) uint {
+	if n < 0 {
+		panic(fmt.Sprintf("suint(%v) expects input >= 0", n))
+	}
+	return uint(n)
+}
+
+// FilterCustomQuery filters all query values starting with `x-`
+func FilterCustomQuery(u *nurl.URL) *nurl.URL {
+	ux := *u
+	vx := make(nurl.Values)
+	for k, v := range ux.Query() {
+		if len(k) <= 1 || k[0:2] != "x-" {
+			vx[k] = v
+		}
+	}
+	ux.RawQuery = vx.Encode()
+	return &ux
+}