[Repo Assist] Fix trailing indented comment after last match clause / DU case de-indented to column 0

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Closes #2653
Closes #2606

Root Cause

When a trailing comment appears after the last match clause or discriminated union case, its range falls outside the range of ExprMatchNode / TypeDefnUnionNode. However, includeTrivia in ASTTransformer.fs extends Oak.Range to cover all code comments, so findNodeWhereRangeFitsIn returns Some(Oak).

simpleTriviaToTriviaInstruction then falls through to the "last child AddAfter" path and attaches the comment as ContentAfter on ModuleOrNamespaceNode (indent = 0), causing it to be printed at column 0 instead of its original column.

Before:

let x =
    match 1 with
    | 1 -> 1
    | 2 -> 2
// | Value3 -> 3   ← de-indented to column 0

After:

let x =
    match 1 with
    | 1 -> 1
    | 2 -> 2
    // | Value3 -> 3   ← correct column 4
```

## Fix

**`Trivia.fs`**: Added `findNodeEndingOnLine` (shallowest-first traversal). Before falling back to the `ModuleOrNamespaceNode` attachment, `simpleTriviaToTriviaInstruction` now checks for a node that ends on the line immediately above the comment and whose start column matches. Shallowest-first ensures we find `ExprMatchNode` (or `TypeDefnUnionNode`) rather than a deeply nested child token that happens to share the same end position.

**`CodePrinter.fs`**: `addFinalNewline` previously checked only the head `WriterEvent`. Because `WriteLineBecauseOfTrivia` is now emitted inside `atCurrentColumn`, structural `RestoreAtColumn`/`RestoreIndent` events appear after it. Updated `addFinalNewline` to skip those non-content events (matching the approach already used by `lastWriteEventIsNewline`) so no extra blank line is appended.

## Tests Added

- `PatternMatchingTests.fs`: "trailing indented comment after last match clause preserves indentation, 2653"  
- `UnionTests.fs`: "trailing indented comment after last union case preserves indentation, 2606"

## Test Status

```
dotnet test artifacts/bin/Fantomas.Core.Tests/debug/Fantomas.Core.Tests.dll

Passed! - Failed: 0, Passed: 2742, Skipped: 7, Total: 2749, Duration: 11s

All 2742 tests pass including the two new regression tests.

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[nojaf]

Insufficient