feat(crawler): add MHTML capture functionality

Add ability to capture web pages as MHTML format, which includes all page resources
in a single file. This enables complete page archival and offline viewing.

- Add capture_mhtml parameter to CrawlerRunConfig
- Implement MHTML capture using CDP in AsyncPlaywrightCrawlerStrategy
- Add mhtml field to CrawlResult and AsyncCrawlResponse models
- Add comprehensive tests for MHTML capture functionality
- Update documentation with MHTML capture details
- Add exclude_all_images option for better memory management

Breaking changes: None

docs/md_v2/api/crawl-result.md

@@ -15,6 +15,7 @@ class CrawlResult(BaseModel):
     downloaded_files: Optional[List[str]] = None
     screenshot: Optional[str] = None
     pdf : Optional[bytes] = None
+    mhtml: Optional[str] = None
     markdown: Optional[Union[str, MarkdownGenerationResult]] = None
     extracted_content: Optional[str] = None
     metadata: Optional[dict] = None
@@ -236,7 +237,16 @@ if result.pdf:
         f.write(result.pdf)
 ```
 
-### 5.5 **`metadata`** *(Optional[dict])*  
+### 5.5 **`mhtml`** *(Optional[str])*  
+**What**: MHTML snapshot of the page if `capture_mhtml=True` in `CrawlerRunConfig`. MHTML (MIME HTML) format preserves the entire web page with all its resources (CSS, images, scripts, etc.) in a single file.  
+**Usage**:
+```python
+if result.mhtml:
+    with open("page.mhtml", "w", encoding="utf-8") as f:
+        f.write(result.mhtml)
+```
+
+### 5.6 **`metadata`** *(Optional[dict])*  
 **What**: Page-level metadata if discovered (title, description, OG data, etc.).  
 **Usage**:
 ```python
@@ -304,11 +314,13 @@ async def handle_result(result: CrawlResult):
     if result.extracted_content:
         print("Structured data:", result.extracted_content)
     
-    # Screenshot/PDF
+    # Screenshot/PDF/MHTML
     if result.screenshot:
         print("Screenshot length:", len(result.screenshot))
     if result.pdf:
         print("PDF bytes length:", len(result.pdf))
+    if result.mhtml:
+        print("MHTML length:", len(result.mhtml))
 ```
 
 ---

docs/md_v2/api/parameters.md

@@ -140,6 +140,7 @@ If your page is a single-page app with repeated JS updates, set `js_only=True` i
 | **`screenshot_wait_for`**                  | `float or None`     | Extra wait time before the screenshot.                                                                    |
 | **`screenshot_height_threshold`**          | `int` (~20000)      | If the page is taller than this, alternate screenshot strategies are used.                                |
 | **`pdf`**                                  | `bool` (False)      | If `True`, returns a PDF in `result.pdf`.                                                                 |
+| **`capture_mhtml`**                        | `bool` (False)      | If `True`, captures an MHTML snapshot of the page in `result.mhtml`. MHTML includes all page resources (CSS, images, etc.) in a single file. |
 | **`image_description_min_word_threshold`** | `int` (~50)         | Minimum words for an image’s alt text or description to be considered valid.                              |
 | **`image_score_threshold`**                | `int` (~3)          | Filter out low-scoring images. The crawler scores images by relevance (size, context, etc.).              |
 | **`exclude_external_images`**              | `bool` (False)      | Exclude images from other domains.                                                                        |