Fix long string overlay in debugger Variables panel (#7112) (#9745)

this PR fixes issue #7112 
In the debugger Variables panel, when a variable's value is a long string (e.g. a URL), it was wrapping to the next line and visually overlaying the next item's controls. The TreeView uses a fixed row height of 20px via itemExtent, but `Text.rich` widgets inside `DisplayProvider` and `DapDisplayProvider` had no single-line constraint.

now this issue is fixed by adding `maxLines: 1`, `softWrap: false`, `overflow: TextOverflow.ellipsis` to all relevant `Text.rich` widgets.
Literal newlines are replaced with `\\n` for visibility and values are wrapped in DevToolsTooltip so the full value is accessible on hover.
A widget test was added in `test/screens/debugger/debugger_screen_dap_variables_test.dart` that pumps a DAP variable node with a 1000-character value and asserts single-line truncation properties and the tooltip carrying the full value.

before this fix Long URL wraps to next line, overlaying next item's controls 

<img width="472" height="124" alt="image" src="https://github.com/user-attachments/assets/abada05b-ccb0-458c-a6b0-26f12c9175ad" />

after this fix Long URL truncated with ... on a single line, hover shows full value
screenshot for reference  

<img width="538" height="590" alt="image" src="https://github.com/user-attachments/assets/c6c3f2ee-efe9-4d7c-afc5-9d7894ca407f" />

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