Fix FileText status code and unify request body size limits

- FileText: now respects the provided status code instead of defaulting to 200 OK
- Request body limits: prepareRequestBody() is now only called when MaxRequestBodySize > 0
  - ShouldBindJSON, ShouldBindWANF, ShouldBindGOB, ShouldBindForm, GetReqBody, PostForm
    all now use the original c.Request.Body path when no limit is configured
- maxBytesReader: fixed exact-limit boundary case where body size == limit was
  incorrectly rejected
- Added regression tests for FileText status codes and body limit behavior

All existing tests pass, and new tests verify the corrected behavior.

context_bodylimit_test.go

@@ -0,0 +1,125 @@
+package touka
+
+import (
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestFileTextUsesProvidedStatusCode(t *testing.T) {
+	t.Helper()
+
+	dir := t.TempDir()
+	filePath := filepath.Join(dir, "hello.txt")
+	if err := os.WriteFile(filePath, []byte("hello touka"), 0o644); err != nil {
+		t.Fatalf("write temp file: %v", err)
+	}
+
+	rr := httptest.NewRecorder()
+	c, _ := CreateTestContext(rr)
+
+	c.FileText(http.StatusCreated, filePath)
+
+	if rr.Code != http.StatusCreated {
+		t.Fatalf("expected status %d, got %d", http.StatusCreated, rr.Code)
+	}
+	if got := rr.Header().Get("Content-Type"); got != "text/plain; charset=utf-8" {
+		t.Fatalf("unexpected content type: %q", got)
+	}
+	if body := rr.Body.String(); body != "hello touka" {
+		t.Fatalf("unexpected body: %q", body)
+	}
+}
+
+func TestMaxBytesReaderAllowsExactLimit(t *testing.T) {
+	t.Helper()
+
+	reader := NewMaxBytesReader(io.NopCloser(strings.NewReader("abcd")), 4)
+	defer reader.Close()
+
+	data, err := io.ReadAll(reader)
+	if err != nil {
+		t.Fatalf("expected exact limit read to succeed, got %v", err)
+	}
+	if string(data) != "abcd" {
+		t.Fatalf("unexpected data: %q", string(data))
+	}
+}
+
+func TestMaxBytesReaderRejectsOverLimit(t *testing.T) {
+	t.Helper()
+
+	reader := NewMaxBytesReader(io.NopCloser(strings.NewReader("abcde")), 4)
+	defer reader.Close()
+
+	_, err := io.ReadAll(reader)
+	if !errors.Is(err, ErrBodyTooLarge) {
+		t.Fatalf("expected ErrBodyTooLarge, got %v", err)
+	}
+}
+
+func TestShouldBindJSONHonorsMaxRequestBodySize(t *testing.T) {
+	t.Helper()
+
+	body := strings.NewReader(`{"name":"abcdef"}`)
+	req := httptest.NewRequest(http.MethodPost, "/json", body)
+	req.Header.Set("Content-Type", "application/json")
+
+	c, _ := CreateTestContextWithRequest(httptest.NewRecorder(), req)
+	c.SetMaxRequestBodySize(8)
+
+	var payload struct {
+		Name string `json:"name"`
+	}
+
+	err := c.ShouldBindJSON(&payload)
+	if !errors.Is(err, ErrBodyTooLarge) {
+		t.Fatalf("expected ErrBodyTooLarge, got %v", err)
+	}
+}
+
+func TestShouldBindFormHonorsMaxRequestBodySize(t *testing.T) {
+	t.Helper()
+
+	body := strings.NewReader("name=abcdef")
+	req := httptest.NewRequest(http.MethodPost, "/form", body)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	c, _ := CreateTestContextWithRequest(httptest.NewRecorder(), req)
+	c.SetMaxRequestBodySize(4)
+
+	var payload struct {
+		Name string `form:"name"`
+	}
+
+	err := c.ShouldBindForm(&payload)
+	if !errors.Is(err, ErrBodyTooLarge) {
+		t.Fatalf("expected ErrBodyTooLarge, got %v", err)
+	}
+}
+
+func TestPostFormHonorsMaxRequestBodySize(t *testing.T) {
+	t.Helper()
+
+	body := strings.NewReader("name=abcdef")
+	req := httptest.NewRequest(http.MethodPost, "/form", body)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	c, _ := CreateTestContextWithRequest(httptest.NewRecorder(), req)
+	c.SetMaxRequestBodySize(4)
+
+	if got := c.PostForm("name"); got != "" {
+		t.Fatalf("expected empty value on over-limit form body, got %q", got)
+	}
+	if len(c.Errors) == 0 {
+		t.Fatal("expected parse error to be recorded")
+	}
+	if !errors.Is(c.Errors[0], ErrBodyTooLarge) {
+		t.Fatalf("expected recorded error to wrap ErrBodyTooLarge, got %v", c.Errors[0])
+	}
+}