Add a setting to scope the query CodeLens to the active query

Follow-up to #125 (closed).

Context

#125 prototyped restricting the query action CodeLens to the active query block, plus a few related tweaks. The design feedback on that PR was that the change should not be unconditional — @danield137 agreed that shipping it behind a setting works. The branch has also drifted out of date with main, so the work is being re-done on a fresh branch rather than rebased.

Scope

Add an opt-in setting that controls whether the query action CodeLens is shown for every query block in the file (current behavior) or only for the query block containing the cursor/selection.

Behaviors from the original prototype worth carrying over:

• CodeLens scoped to the active query range, driven by cursor position, selection, multi-selection, reversed selection, and range boundaries.
• Running indicator stays visible when focus moves away from a running query.
• The queryRangeScope helper and its unit tests (cursor, selection, multi-selection, reversed selection, boundary cases) were the reusable part of #125.

Notes

• The separator-styling changes bundled into #125 are a separate concern; they should not ride along with this setting.
• Original prototype for reference: https://github.com/microsoft/Kusto-Explorer-VsCode/pull/125

Start by reviewing the original prototype in pull request #125 and locate the query CodeLens implementation, the proposed queryRangeScope helper, and its unit tests. Add an opt-in setting that switches between all query blocks and the active cursor/selection range, while preserving the running indicator and excluding separator styling; done means the listed cursor, selection, multi-selection, reversed-selection, and boundary tests pass.