Whole-suite history chart: subtract /encoding/ from the run totals

[nicoburns]

Summary

On /wpt?range=all browser lines went to ~200%: the whole-suite union total from the comparison DB (~1.12M subtests) leaves out /encoding/ (which the ingester skips as very large and not layout-relevant), but browser-wpt-results' total.json counts it (~1.15M subtests on its own), so passed counts exceeded the denominator.

Fix: the whole-suite history is now total.json − areas/encoding.json per run, so it covers the same tests as the DB total it is divided by.

// wpt_summaries
SummaryCacheEntry::total_history_without_encoding(product, union_total)
// = history("") with each run's ScoreTuple reduced by that run's encoding tuple
//   (run missing encoding data => no score; product with no encoding file,
//   i.e. Blitz => unchanged)

// main.rs compare_history: used when area == "", and the encoding area is
// added to the summary requests for each product

Sanity check with current data: Chrome 2,269,986 − 1,152,348 = 1,117,638 vs DB union total 1,119,347 → 99.8%.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/6a70291c2fd54da1a02968bb80f8622b
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/6a70291c2fd54da1a02968bb80f8622b?variant=devin-insiders
Requested by: @nicoburns

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