test(plot): pin the hot-handle re-index on region removal, refresh coverage

`remove_region()` now clears or decrements the published `hot_.region` with the
cache it re-indexes, so a frame after a removal highlights the region the handle
actually names. The new case covers both branches (a handle above the hole
follows it down, the removed region's handle is cleared with its zone), and the
coverage document is regenerated by the command that measured it: 95.2% of src/,
every file at or above 80%.

docs/coverage.md

@@ -43,7 +43,7 @@ when one is missing.
 <!-- BEGIN GENERATED: tools/coverage.sh -->
 
 ```
-coverage_floor: ok -- 23 files under src/, aggregate 95.3% lines (3284/3447), every file at or above 80%, aggregate target 90%
+coverage_floor: ok -- 23 files under src/, aggregate 95.2% lines (3302/3469), every file at or above 80%, aggregate target 90%
 ```
 
 | File | Lines | Line rate | Functions |
@@ -54,24 +54,24 @@ coverage_floor: ok -- 23 files under src/, aggregate 95.3% lines (3284/3447), ev
 | `src/data/stream_series.cpp` | 39/39 | 100.0% | 100.0% |
 | `src/gl/handle.cpp` | 256/256 | 100.0% | 100.0% |
 | `src/gl/loader.cpp` | 81/81 | 100.0% | 100.0% |
-| `src/input/controller.cpp` | 327/341 | 95.9% | 100.0% |
+| `src/input/controller.cpp` | 329/343 | 95.9% | 100.0% |
 | `src/math/transform.cpp` | 28/28 | 100.0% | 100.0% |
 | `src/plot/axis.cpp` | 12/12 | 100.0% | 100.0% |
-| `src/plot/figure.cpp` | 213/218 | 97.7% | 95.5% |
+| `src/plot/figure.cpp` | 218/223 | 97.8% | 95.5% |
 | `src/plot/grid.cpp` | 15/16 | 93.8% | 100.0% |
 | `src/plot/measure.cpp` | 21/21 | 100.0% | 100.0% |
-| `src/plot/plot.cpp` | 733/753 | 97.3% | 98.9% |
+| `src/plot/plot.cpp` | 743/763 | 97.4% | 98.9% |
 | `src/plot/ticks.cpp` | 93/99 | 93.9% | 100.0% |
 | `src/render/buffer.cpp` | 88/98 | 89.8% | 100.0% |
 | `src/render/embedded_mono_font.cpp` | 45/45 | 100.0% | 100.0% |
 | `src/render/primitives.cpp` | 71/75 | 94.7% | 100.0% |
 | `src/render/program.cpp` | 26/27 | 96.3% | 100.0% |
-| `src/render/renderer.cpp` | 529/604 | 87.6% | 93.7% |
+| `src/render/renderer.cpp` | 530/609 | 87.0% | 93.7% |
 | `src/render/text.cpp` | 27/30 | 90.0% | 100.0% |
 | `src/render/text_atlas.cpp` | 40/41 | 97.6% | 100.0% |
 | `src/render/vertex_array.cpp` | 59/59 | 100.0% | 100.0% |
 | `src/text/true_type_font.cpp` | 270/291 | 92.8% | 96.8% |
-| **src/ aggregate** | **3284/3447** | **95.3%** | **98.3%** |
+| **src/ aggregate** | **3302/3469** | **95.2%** | **98.3%** |
 
 <!-- END GENERATED: tools/coverage.sh -->