Improve branch and path coverage presentation in HTML report

[sebastianbergmann]

This intends to make the branch and path coverage views in the HTML code coverage report significantly easier to read and act on.

Source view gutter column

All three source views (line, branch, path) now include a narrow gutter column between the line number and the source code.

In the branch view, this column displays the direction indicators described above. In the line and path views, the column is present but hidden to keep the layout consistent across view tabs.

Inline branch direction indicators

The branch coverage source view now shows colored markers in the gutter at decision-point lines (lines where code can take multiple directions, such as if / else expressions). Each marker represents one branch direction: green for covered, red for uncovered.

Coverage badges on method headings

Each method heading in the branch and path structure sections now shows a coverage badge color-coded green, yellow, or red. This provides a quick at-a-glance summary of how well each method's branches or paths are covered, without needing to scan through the full table.

Path rendering no longer refuses to render

Previously, methods with more than 100 code paths showed only a message saying "too many paths to sensibly render." Now the full path table is always rendered. For methods with many paths, the table is wrapped in a collapsible section (collapsed by default) so the page remains navigable while still providing access to all the data.

[codecov]

Codecov Report

❌ Patch coverage is 96.66667% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.97%. Comparing base (d92877a) to head (59f5c88).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/Report/Html/ControlFlowGraph.php	94.95%	6 Missing ⚠️
src/Report/Html/Renderer/File.php	97.77%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1141      +/-   ##
============================================
+ Coverage     96.91%   96.97%   +0.05%     
- Complexity     1478     1529      +51     
============================================
  Files           109      110       +1     
  Lines          5020     5218     +198     
============================================
+ Hits           4865     5060     +195     
- Misses          155      158       +3     

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[sebastianbergmann]

Both #1140 and this have the same ancestor, but #1140 is the bigger change and should be merged first, in case both #1140 and this will be merged.