feat(go-config): multi-format codecs, envc CLI, fixtures, ASRs

- Module github.com/eslider/go-config with env/yaml/json/ini packages
- internal: source, keymap, merge, structconv, bytesutil
- cmd/envc: convert, get, merge
- docs/asr ASR-0001..0008, README/CHANGELOG/AGENTS refresh
- golangci-lint v2 config; tests + fixtures

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/bytesutil/read.go

@@ -0,0 +1,19 @@
+// Package bytesutil reads entire sources into memory.
+package bytesutil
+
+import (
+	"context"
+	"io"
+
+	"github.com/eslider/go-config/internal/source"
+)
+
+// ReadAll reads and closes the stream opened by s.
+func ReadAll(ctx context.Context, s source.Source) ([]byte, error) {
+	rc, err := s.Open(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = rc.Close() }()
+	return io.ReadAll(rc)
+}