Fix AST viewer and contextual query caches when refreshing test databases

[josefs]

Fixes #3758

When an imported .testproj test database is reimported after running codeql test run --keep-databases, the old database item is removed and the updated database is copied into the same storage path (producing the same codeql-zip-archive:// source file URIs).

Previously, View CFG updated properly because TemplatePrintCfgProvider only cached the resolved query path and template parameters while re-evaluating PrintCfg.ql on every invocation. In contrast, TemplatePrintAstProvider (as well as TemplateQueryDefinitionProvider and TemplateQueryReferenceProvider) cached evaluated results in CachedOperation keyed by fileUri.toString():

1. Their caches were never cleared when a database item was removed (DatabaseEventKind.Remove), so View AST continued returning stale AST results after refreshing a test database.
2. When a file's AST or definitions/references were already cached, provideAst / provideDefinition / provideReferences returned the cached entry without running a query, bypassing DatabaseManager.maybeReimportTestDatabase and never prompting to reimport an outdated test database.

Changes

• Added CachedOperation.has() to check whether a key is currently cached.
• Registered a dbm.onDidChangeDatabaseItem listener on TemplatePrintAstProvider, TemplateQueryDefinitionProvider, TemplateQueryReferenceProvider, and TemplatePrintCfgProvider to reset their caches on DatabaseEventKind.Remove.
• Checked dbm.maybeReimportTestDatabase before serving cached results in TemplatePrintAstProvider, TemplateQueryDefinitionProvider, and TemplateQueryReferenceProvider.
• Added tests in template-provider.test.ts and cached-operation.test.ts.

[Copilot]

🟡 Changes recommended

Concurrent cache hits can trigger overlapping destructive database reimports.

1 open finding

• Serialize concurrent database reimport checks per URI · New

What changed in this PR

Fixes stale contextual-query results after test database reimports.

Changes:

• Invalidates provider caches when databases are removed.
• Checks for outdated test databases before returning cached results.
• Adds cache and provider tests.

File	Description
template-provider.ts	Adds invalidation and reimport checks.
cached-operation.ts	Adds cache-key inspection.
template-provider.test.ts	Tests provider cache refresh behavior.
cached-operation.test.ts	Tests cache lookup and reset behavior.

🧠 Review effort: Balanced

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[josefs]

The cache is hit so seldomly, I don't imagine this ever being a problem.