feat: expose Playwright launch params in BrowserConfig (#1820)

[hafezparast]

Summary

• Adds 4 new params to BrowserConfig for custom browser binary support
• All defaults unchanged — fully backward compatible
• Addresses all 6 items from the feature request (2 were already done)

Closes discussion #1820

New Parameters

Param	Type	Default	Purpose
executable_path	str	None	Path to custom Chromium binary
ignore_default_args	list	None	Playwright flags to exclude from launch
skip_default_browser_args	bool	False	Skip all hardcoded args, use only extra_args
skip_default_headers	bool	False	Skip forced User-Agent/sec-ch-ua overrides

Usage

# Custom stealth binary — full control
config = BrowserConfig(
    executable_path="/usr/bin/brave-browser",
    skip_default_browser_args=True,
    skip_default_headers=True,
    extra_args=["--window-size=1920,1080"],
)

Already covered (no changes needed)

• device_scale_factor — already configurable (PR Add configurable device_scale_factor for improved screenshot quality #1463)
• override_navigator=False — already on CrawlerRunConfig

Test plan

• All 4 params default correctly (None/False)
• Explicit param setting works
• to_dict() / load() roundtrip preserves all params
• clone() preserves and overrides correctly
• _build_browser_args(): default includes hardcoded args
• _build_browser_args(): skip_default_browser_args=True → only extra_args
• _build_browser_args(): executable_path / ignore_default_args passed to launch dict
• ManagedBrowser.build_browser_flags(): same skip logic works
• setup_context(): default sets User-Agent headers
• setup_context(): skip_default_headers=True skips UA override
• setup_context(): custom headers still work with skip
• Regression: 58 passed, 5 skipped across 3 test suites

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