refactor(httpheader): extract header parsing into dedicated package

Moved HTTP header parsing and building logic from server package to internal/httpheader

internal/httpheader/header.go

@@ -0,0 +1,30 @@
+package httpheader
+
+type ResponseHeader interface {
+	Value(key string) string
+	Set(key string, value string)
+	Remove(key string)
+	Finalize() []byte
+}
+
+type responseHeader struct {
+	startLine []byte
+	headers   map[string]string
+}
+
+type RequestHeader interface {
+	Value(key string) string
+	Set(key string, value string)
+	Remove(key string)
+	Finalize() []byte
+	GetMethod() string
+	GetPath() string
+	GetVersion() string
+}
+type requestHeader struct {
+	method    string
+	path      string
+	version   string
+	startLine []byte
+	headers   map[string]string
+}