Support per-folder enable/disable for the singleton server in multi-root workspaces

[Copilot]

Tool extensions consuming this library risk redundant LSP processes and duplicated diagnostics in multi-root workspaces. The TypeScript client already runs a singleton server (one client rooted at getProjectRoot(), per-folder settings forwarded via getExtensionSettings()), so the gap was the lack of a per-folder opt-out (e.g. pylint.enabled: false for a single folder).

Changes

• settings.ts
  • isToolEnabledForWorkspace(namespace, workspace?, settingKey?) — reads the per-folder <namespace>.enabled boolean; defaults to enabled, settingKey overridable (e.g. 'enable').
  • getEnabledWorkspaceFolders(namespace, settingKey?) — folders for which the tool is enabled.
  • getExtensionSettings() now resolves settings only for enabled folders, so the shared server never lints opted-out folders. Backward compatible: unset → enabled.
• index.ts — export the two new helpers.
• Tests — cover default-enabled, explicit disable, custom setting key, and folder filtering through getExtensionSettings.
• README — document the singleton model and per-folder enable API.

Example

// Disabled folders are omitted; the singleton server only receives enabled ones.
const settings = await getExtensionSettings('pylint', toolConfig, resolveInterpreter);

// Or query directly when registering per-folder providers:
const folders = getEnabledWorkspaceFolders('pylint');
const enabled = isToolEnabledForWorkspace('pylint', folder, 'enable');

Note: getExtensionSettings() filtering changes which folders reach the server when a tool exposes an enabled setting and a user disables a folder — worth a careful look during review, though defaults preserve existing behavior.