Improve image checker

[forsyth2]

Summary

This PR is specifically to speed up analysis of existing image checker tests. It will likely replace #685 and #695 completely, but ultimately #520/#698 will be needed to 1) automate the pre-test runs of zppy itself and 2) test many more cfg files than the existing ones tested by the image checker.

Objectives:

• Add the ability to test UNIQUE_IDs other than the one on the current branch.
• Consolidate test info and create a markdown results table automatically, as in Automate organization of test results #695, rather than needing to parse for information manually.
• Automatically print lists of missing/mismatched files, as in Automate testing of specific cases #698
• [cancelled for this PR] Automatically create image diff grid, as in Script to generate image diff grid #685.

Issue resolution:

• On the path to resolving Further automate tests #516.

Select one: This pull request is...

• a bug fix: increment the patch version
• a small improvement: increment the minor version
• a new feature: increment the minor version [Testing only]
• an incompatible (non-backwards compatible) API change: increment the major version

Small Change

• To merge, I will use "Squash and merge". That is, this change should be a single commit.
• Logic: I have visually inspected the entire pull request myself.
• Pre-commit checks: All the pre-commits checks have passed.

[forsyth2]

Using the code as of 4e3d5b3, this is the min_summary.md result:

Summary of test results

Diff subdir is where to find the lists of missing/mismatched images, the image diff grid, and the individual diffs.
Note image diff grids can not yet be constructed automatically.

Test name	Total images	Correct images	Missing images	Mismatched images	Diff subdir
comprehensive_v2_e3sm_diags	2921	2875	0	46	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v2_www/test_zppy_20250401/v2.LR.historical_0201/image_check_failures_comprehensive_v2_test_pr699_try6/e3sm_diags
comprehensive_v2_mpas_analysis	854	854	0	0	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v2_www/test_zppy_20250401/v2.LR.historical_0201/image_check_failures_comprehensive_v2_test_pr699_try6/mpas_analysis
comprehensive_v2_global_time_series	6	1	0	5	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v2_www/test_zppy_20250401/v2.LR.historical_0201/image_check_failures_comprehensive_v2_test_pr699_try6/global_time_series
comprehensive_v2_ilamb	482	482	0	0	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v2_www/test_zppy_20250401/v2.LR.historical_0201/image_check_failures_comprehensive_v2_test_pr699_try6/ilamb
comprehensive_v3_e3sm_diags	3750	3696	0	54	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v3_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_comprehensive_v3_test_pr699_try6/e3sm_diags
comprehensive_v3_mpas_analysis	854	854	0	0	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v3_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_comprehensive_v3_test_pr699_try6/mpas_analysis
comprehensive_v3_global_time_series	15	1	0	14	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v3_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_comprehensive_v3_test_pr699_try6/global_time_series
comprehensive_v3_ilamb	512	512	0	0	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v3_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_comprehensive_v3_test_pr699_try6/ilamb
bundles_e3sm_diags	1472	1472	0	0	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_bundles_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_bundles_test_pr699_try6/e3sm_diags
bundles_global_time_series	3	1	0	2	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_bundles_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_bundles_test_pr699_try6/global_time_series
bundles_ilamb	241	241	0	0	/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_bundles_www/test_zppy_20250401/v3.LR.historical_0051/image_check_failures_bundles_test_pr699_try6/ilamb

[forsyth2]

To convert to web pages:

/lcrc/group/e3sm/public_html/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v2_www/test_zppy_20250401/v2.LR.historical_0201/image_check_failures_comprehensive_v2_test_pr699_try6/e3sm_diags

would become https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.forsyth2/zppy_weekly_comprehensive_v2_www/test_zppy_20250401/v2.LR.historical_0201/image_check_failures_comprehensive_v2_test_pr699_try6/e3sm_diags/

[forsyth2]

These numbers actually do match the numbers in #634 (comment), so it appears to be working as intended.

Since this PR only touches testing code (i.e., not user-facing code), and I am the primary user for these changes, no further review is necessary. I do hope to make several more testing updates (e.g., #685, #520/#698), but this PR is an important step forward in automating the testing process.