fix(core): retry failed ripgrep resolution and sanitize PowerShell 5.1 module path on Windows - #41015

Summary

Fixes both root causes of grep/glob failing on Windows from #40623:

• Failed ripgrep resolution was cached forever. RipgrepBinary.filepath wrapped the locate/download/extract effect in Effect.cached, which memoizes failures as well as successes. A single failed download or extraction (e.g. the PowerShell issue below) poisoned every grep/glob call in that process — even after the user fixed the environment (e.g. placed rg.exe in ~/.cache/opencode/bin/) — until opencode was restarted. Replaced with a single-flight memo that caches only successful resolutions, so the next call retries.
• Zip extraction breaks when launched from MSIX PowerShell 7. Extraction spawns powershell.exe (Windows PowerShell 5.1) with Expand-Archive, and the child inherits PSModulePath from the launching shell. When opencode is started from the Microsoft Store (MSIX) build of PowerShell 7, that variable lists the Core-edition module directory first; the 5.1 module autoloader deems it incompatible and stops searching, so Expand-Archive fails with CouldNotAutoloadMatchingModule and the downloaded zip is never extracted. The child now gets a pinned PSModulePath pointing at the inbox 5.1 module directory (%SystemRoot%\System32\WindowsPowerShell\v1.0\Modules) when the resolved shell is powershell.exe. pwsh.exe spawns are untouched.

Test

• Added packages/core/test/ripgrep-binary.test.ts:
  • memoizeSuccess memoizes a successful resolution (runs once)
  • memoizeSuccess retries a failed resolution instead of caching the failure, then caches the eventual success
  • windowsPowerShell5ModulePath honors SystemRoot and falls back to C:\Windows
• bun test test/ripgrep.test.ts test/ripgrep-binary.test.ts test/filesystem/search.test.ts — 8 pass / 0 fail
• bun run typecheck (tsgo) — clean
• oxlint — no new warnings (the unbound-method pattern matches the existing Semaphore.makeUnsafe(1).withPermit usage in session/runner/llm.ts)

Refs #40623