Add inline-script cache and interpreter utilities (PEP 723 PR 5b/16)

[StellaHuang95]

Part of #1602 (PEP 723 inline script env support). Design doc: #1601.

Split for review (3 PRs). Reviewers flagged the original PR 5 as too large, so it is split into three stacked PRs grouped by dependency layer:

• 5a — generic env-creation utilities — Add generic environment-creation utilities (PEP 723 PR 5a/16) #1651. Based on main; merges first.
• 5b — inline-script cache + interpreter utilities — this PR (Add inline-script cache and interpreter utilities (PEP 723 PR 5b/16) #1655). Stacked on 5a.
• 5c — create() happy path (manager + wiring) — Add PEP 723 inline script environment creation (PEP 723 PR 5c/16) #1656. Stacked on 5b.

Applied together the three PRs are byte-for-byte identical to the original single change. Merge order: 5a → 5b → 5c.

This PR is stacked on #1651, so the diff below currently also includes the 5a commit. To review just this PR, open the Add inline-script cache and interpreter utilities for creation commit (09b7664, 6 files). Once #1651 merges to main, this PR reduces to its own changes with no rebase needed.

Roadmap context

This is the second slice of PR 5 of 16. See #1651 for the full roadmap table.

Phase 2: Manager	PR	Status
	PR 4: InlineScriptEnvManager skeleton	merged (#1610)
	PR 5a: generic env-creation utilities	#1651
	PR 5b: inline-script cache + interpreter utilities	this PR (#1655)
	PR 5c: create() happy path (manager + wiring)	#1656

Why this PR

With the generic primitives from 5a in place, this PR lands the inline-script-specific utilities that create() (5c) composes: a normalized dependency cache key, cache-layout ownership/status checks, and interpreter-constraint handling. These are pure functions with no manager wiring yet, so they are reviewed on their own.

What this PR adds

Cache-key tail normalization (src/common/inlineScriptCacheKey.ts): adds normalizeRequirementTail, a quote-aware scanner that collapses whitespace and tightens comparator spacing (>= 1.0 → >=1.0) in a requirement's version/marker tail while preserving quoted PEP 508 marker literals verbatim (e.g. python_version >= "3.11"). Direct-reference requirements (pkg @ https://…) are kept verbatim after the name and extras. The effect is that semantically identical dependency strings normalize to the same cache key, so they reuse the same cached environment.

Cache-layout additions (src/common/inlineScriptCacheLayout.ts): resolveCacheEntryPath (containment under the cache root), inspectOwnedCacheEntry (realpath ownership), getBaseInterpreterStatus (available | missing | unavailable), inspectMetaJson (typed sidecar read), and a stricter validateMeta. The .meta.json sidecar schema is { schemaVersion, baseInterpreterPath, baseInterpreterVersion, lastUsedAt }. Uses getVenvPythonPath from 5a (the edge that stacks this PR on #1651).

Interpreter-constraint trimming (src/common/inlineScriptInterpreter.ts): pickCompatibleInterpreter now trims requires-python, so a whitespace-only constraint is treated as no constraint.

Tests

• inlineScriptCacheKey.unit.test.ts — canonicalization cases including marker literals and direct references.
• inlineScriptCacheLayout.unit.test.ts — the new containment, ownership, base-interpreter-status, and typed sidecar-read helpers.
• inlineScriptInterpreter.unit.test.ts — constraint trimming / selection.

On this branch (5a + 5b) npm run compile-tests is clean and npm run unittest reports 1465 passing, 0 failing, 5 pending.

User impact

None. These are pure utilities. Nothing calls the new code paths until the manager lands in 5c (#1656).

Merge order

Merge #1651 first, then this PR, then #1656.