feat: placement strategies for next edit to avoid it going off screen

[sestinj]

Description

Still needs work. The setup for placement strategies seems to be right, but the second strategy doesn't seem to function. 30min of debugging will probably do it, I'll hopefully get around to this soon.

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Checklist

• [] I've read the contributing guide
• [] The relevant docs, if any, have been updated or created
• [] The relevant tests, if any, have been updated or created

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Tests

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Summary by cubic

Keeps the Next Edit tooltip on-screen by choosing a nearby anchor line and horizontal padding that fit within the viewport. Introduces a pluggable placement strategy and sets a viewport-aware default.

• New Features

  • Added NextEditPlacementStrategy with a ViewportAwarePlacementStrategy default.
  • Strategy picks an anchor line near the cursor (prefers visible lines) and computes padding to avoid horizontal overflow using editor.wordWrapColumn (fallback 100).
  • NextEditWindowManager now uses the strategy, clamps results, anchors at end-of-line, and converts padding to left margin.

• Bug Fixes

  • Prevents the Next Edit tooltip from rendering off-screen and handles document churn by clamping line and padding.
  • GitHub workflow: added idempotency-key to review sessions to avoid duplicate runs.