Drop Jurassic from engine comparison benchmarks, add Okojo

[lahma]

Jurassic hasn't seen much traction or updates and is ES5-only, so this drops it from the engine comparison benchmark and brings in a fresh contender: Okojo 0.1.2-preview.1, a new low-allocation, AOT-friendly bytecode engine for .NET 10.

What changed

• Directory.Packages.props / Jint.Benchmark.csproj / dependabot.yml — remove Jurassic, add Okojo.
• EngineComparisonBenchmark — replace the Jurassic lane with two Okojo lanes following the same rules as the other engines:
  • Okojo — fresh JsRuntime.Create() + Execute(source) each iteration (parses + compiles + runs), mirroring the plain Jint / NilJS / YantraJS lanes.
  • Okojo_Prepared — reuses the parsed program (JavaScriptParser.ParseScript → JsProgram, Okojo's realm-independent artifact) and compiles + runs the bytecode against each iteration's own fresh realm. Its gap to Okojo is parsing cost — the direct analog of Jint_ParsedScript. The compiled JsScript is realm-bound (JsCompiler.Compile(realm, program)), so it is intentionally not cached across the fresh runtimes, which would otherwise execute against a shared setup realm and violate the fresh-engine-per-iteration rule.
• Okojo has no engine-level strict switch, so global strict mode is enabled with a leading "use strict" directive (verified genuinely enforced); all 21 scripts run under it.
• Program.cs smoke-comparison lane swapped Jurassic → Okojo.

Benchmarks

Only the Okojo lanes were re-measured (same machine + .NET runtime as the 4.12.0 run) and merged into the table, keeping thermal noise low; the other engines' numbers are unchanged. With Jurassic gone and every remaining engine parsing ES2015+, there are no more NA rows on the -modern scripts.

Where Okojo lands: mid-pack. It never tops a row, is the fastest non-Jint engine on the dromaeo-object-string rows, and is a genuinely frugal allocator (it edges Jint on the object-array workloads), but it trails the field on regex-heavy work. Jint remains the fastest engine on 17 of 21 scripts and the fastest interpreter on all 21.

The README also now notes how each engine executes — Jint (tree-walking AST interpreter), NiL.JS (interpreter), Okojo (bytecode VM interpreter), YantraJS (compiles to .NET IL) — since only the IL compiler runs ahead on tight numeric/call loops.

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