fix(ci): resolve test count inconsistencies in reporting scripts

[hhimanshu]

Summary

• Removes the hardcoded 65 properties × 500 cases = 32,500 line from post-conformance-comment.sh — there are now 132 property test functions (×500 = 66,000 cases), so the old number was wrong. The breakdown already appears correctly in the coverage comment which reads junit.xml dynamically.
• Adds nextest_total to post-coverage-comment.sh and generate-pages-html.py by summing testsuite/@tests from junit.xml at runtime.
• Adds an "About the totals" note to both the PR coverage comment footer and the GitHub Pages explainer, clarifying that the ~76,988 grand total counts formula evaluations while the GitHub Checks badge reports Rust #[test] functions — two intentionally different metrics.

Closes #518

Before / After

Before: conformance PR comment said "32,500 property inputs"; coverage comment said "66,000 (132×500)". Pages had no explanation for why Checks showed 2,879.

After: conformance comment no longer mentions property tests (the coverage comment covers it); coverage comment footer and Pages explainer both state the nextest count and explain the difference.

Test plan

• bash -n passes on both shell scripts
• python3 -c "import ast; ast.parse(...)" passes on generate-pages-html.py
• CI green on this PR

🤖 Generated with Claude Code

[github-actions]

Test Coverage by Category

Category	Unit Tests	Google Sheets Conformance	Property Cases	Total
Array	42	301/301 ✓	1,000 (2×500)	1,343
Database	35	175/175 ✓	3,500 (7×500)	3,710
Date	348	295/295 ✓	2,500 (5×500)	3,143
Engineering	245	841/841 ✓	5,500 (11×500)	6,586
Filter	11	20/20 ✓	4,500 (9×500)	4,531
Financial	149	182/182 ✓	2,000 (4×500)	2,331
Info	0	390/390 ✓	4,500 (9×500)	4,890
Logical	114	250/250 ✓	3,500 (7×500)	3,864
Lookup	69	361/361 ✓	1,000 (2×500)	1,430
Math	528	1,923/1,923 ✓	8,000 (16×500)	10,451
Operator	75	263/263 ✓	7,500 (15×500)	7,838
Parser	80	94/94 ✓	4,000 (8×500)	4,174
Statistical	480	2,557/2,557 ✓	5,000 (10×500)	8,037
Text	305	658/660 ⚠	4,000 (8×500)	4,965
Volatile	0	—	3,500 (7×500)	3,500
Web	29	56/56 ✓	6,000 (12×500)	6,085
Total	2,620	8,366/8,368	66,000 (132×500)	~76,988

_{Oracle: Google Sheets · ✓ = 100% passing · ⚠ = known deviation · The ~76,988 total counts formula evaluations (each conformance row and each property case = 1). GitHub Checks reports 2,879 Rust test functions.}

[github-actions]

Test Coverage by Category

Category	Unit Tests	Google Sheets Conformance	Property Cases	Total
Array	42	301/301 ✓	1,000 (2×500)	1,343
Database	35	175/175 ✓	3,500 (7×500)	3,710
Date	348	295/295 ✓	2,500 (5×500)	3,143
Engineering	245	841/841 ✓	5,500 (11×500)	6,586
Filter	11	20/20 ✓	4,500 (9×500)	4,531
Financial	149	182/182 ✓	2,000 (4×500)	2,331
Info	0	390/390 ✓	4,500 (9×500)	4,890
Logical	114	250/250 ✓	3,500 (7×500)	3,864
Lookup	69	361/361 ✓	1,000 (2×500)	1,430
Math	528	1,923/1,923 ✓	8,000 (16×500)	10,451
Operator	75	263/263 ✓	7,500 (15×500)	7,838
Parser	80	94/94 ✓	4,000 (8×500)	4,174
Statistical	480	2,557/2,557 ✓	5,000 (10×500)	8,037
Text	305	658/660 ⚠	4,000 (8×500)	4,965
Volatile	0	—	3,500 (7×500)	3,500
Web	29	56/56 ✓	6,000 (12×500)	6,085
Total	2,620	8,366/8,368	66,000 (132×500)	~76,988

_{✓ = 100% passing · ⚠ = known deviation · The ~76,988 total counts formula evaluations (each conformance row and each property case = 1). GitHub Checks reports 2,879 Rust test functions: 2,620 unit + 159 property functions (shown as cases above) + 100 conformance/integration.}