Fix child_by_text/child_by_description with allow_scroll_search to return False on .exists instead of raising exception

[Copilot]

child_by_text(allow_scroll_search=True).exists raises UiObjectNotFoundError when element not found, inconsistent with standard selector behavior where .exists returns boolean.

# Before: raises UiObjectNotFoundError
d(resourceId="id/listView").child_by_text("Movies", allow_scroll_search=True).exists

# After: returns False
d(resourceId="id/listView").child_by_text("Movies", allow_scroll_search=True).exists  # False

Changes

• child_by_text() / child_by_description(): Catch UiObjectNotFoundError when allow_scroll_search=True, return UiObject with sentinel selector (text/description="__ui_object_not_found__", instance=sys.maxsize) that evaluates .exists to False
• Backward compatibility: Exception still raised when allow_scroll_search=False (default)
• Tests: Added 4 unit tests covering both methods with/without allow_scroll_search, element found/not found cases

Implementation Notes

• Uses sys.maxsize as sentinel instance to avoid collision with legitimate indices
• Fixed sentinel text prevents issues with special characters in user input
• Maintains lazy evaluation: no RPC call until .exists accessed

Original prompt

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This section details on the original issue you should resolve

<issue_title>child_by_text(allow_scroll_search=True,...).exists 找不到会抛一个 UiObjectNotFoundError 而不是返回对应的布尔值</issue_title>
<issue_description>在使用 child_by_text 方法并开启 allow_scroll_search=True 时，如果滚动到底部依然没有找到目标元素，代码会直接抛出uiautomator2.exceptions.UiObjectNotFoundError 异常。
我认为这与 u2 中其他选择器的 .exists 行为不一致。通常情况下，调用 .exists 属性时，如果元素不存在，应该直接返回 False，而不是中断程序抛出异常。这样就只能使用 try...except 来捕获这个错误才能判断元素不存在，这不太符合 .exists 的设计初衷。
下图125行报错。

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes child_by_text(allow_scroll_search=True,...).exists 找不到会抛一个 UiObjectNotFoundError 而不是返回对应的布尔值 #1160

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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