feat: Add ErrorSnapshotter to ErrorTracker

[Pijukatel]

Description

Added ErrorSnapshotter that can take page snapshot (screenshot or html) on each first encountered unique error.
Added documentation describing how to use it.

Issues

• Closes: Implement ErrorTracker #151

Testing

Added unit tests.
Example PlaywrightCrawler based actor run with ErrorSnapshotter: https://console.apify.com/actors/C0lWh1UCQvgdArp6R/runs/UNuaiRWBDgxiJau0U#storage

[Copilot]

Pull Request Overview

This PR implements an ErrorSnapshotter to capture page snapshots (HTML and screenshot) on the first encountered error and updates error tracking to support asynchronous error handling with snapshot capture. Key changes include:

• Introducing the ErrorSnapshotter class and integrating it within ErrorTracker.
• Updating tests for both Playwright and HTTP crawlers to validate snapshot functionality.
• Refactoring error tracking calls to be asynchronous across the codebase.

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/unit/server_endpoints.py	Adds HTML response constants for server endpoint tests.
tests/unit/server.py	Refactors inline HTML responses to use defined constants.
tests/unit/crawlers/_playwright/test_playwright_crawler.py	Adds tests for snapshot retrieval and error snapshots in the Playwright crawler.
tests/unit/crawlers/_http/test_http_crawler.py	Adds tests to verify snapshot functionality in the HTTP crawler and updates error snapshot test.
tests/unit/_statistics/test_error_tracker.py	Updates tests to use async error tracker methods.
src/crawlee/statistics/_statistics.py	Introduces a new parameter to control error snapshot saving.
src/crawlee/statistics/_error_tracker.py	Refactors the error tracker to support async snapshot capture via ErrorSnapshotter.
src/crawlee/statistics/_error_snapshotter.py	Implements the ErrorSnapshotter class to capture and store HTML and JPEG snapshots.
src/crawlee/crawlers/_playwright/_playwright_pre_nav_crawling_context.py	Adds a get_snapshot method to capture page content and screenshot.
src/crawlee/crawlers/_playwright/_playwright_crawler.py	Modifies context yielding to capture errors for early snapshot collection.
src/crawlee/crawlers/_basic/_context_pipeline.py	Updates pipeline middleware signature to support exception propagation.
src/crawlee/crawlers/_basic/_basic_crawler.py	Updates error tracker calls to be asynchronous in retry and failure scenarios.
src/crawlee/crawlers/_abstract_http/_http_crawling_context.py	Adds a get_snapshot method returning HTML from HTTP responses.
src/crawlee/_types.py	Defines the PageSnapshot data class and updates the BasicCrawlingContext interface.

Comments suppressed due to low confidence (2)

tests/unit/crawlers/_http/test_http_crawler.py:712

• [nitpick] The use of the variable 'key_info' after the for-loop may be unclear. Consider capturing the key from the dictionary explicitly for clarity.

assert key_info.key.endswith('.html')

src/crawlee/statistics/_error_tracker.py:73

• The variable 'new_error_group_message' is initialized to an empty string and never updated, which could lead to confusion. Consider removing it or updating its value if it is intended for wildcard similarity matching.

new_error_group_message = ''  # In case of wildcard similarity match

[vdusek]

LGTM