feat(python-setup): report manual-setup opt-out telemetry - #2170

*Why*
The manual opt-out added in #2158 (databricks.python.environmentSetup:
manual, plus the "Use manual setup" button on the E_FETCH failure) is only
observable today via the generic commandExecution event, and opting out by
editing the setting directly is invisible. We can't measure how often users
fall back to a manually managed environment, or from where.
*What*
- New python_env.manual_setup.optout event, recorded when the opt-out command
 write succeeds, with scope (workspace|global) and source (error_popup|
 command_palette). The E_FETCH popup tags its invocation as error_popup;
 palette invocations read as command_palette.
- Add setupMode (uv | pip | fallback-pip) to the once-per-session
 python_env.setup.detected event so opt-out prevalence is measurable per
 session. Derived in one place (resolveSetupMode, beside isUvSetupSuitable):
 manual => fallback-pip; auto splits by uv-suitability into uv / pip. The
 exact manager stays in primaryManager.
Categorical data only; no paths, package names, or PII.
*Verification*
- yarn build (tsc) and yarn test:lint clean.
- yarn test:unit green (1061 passing). Added unit tests: resolveSetupMode
 cases; recordManualSetupOptout scope/source; emitDetection setupMode for
 uv / pip / fallback-pip; and the popup passing {source: "error_popup"}.
Co-authored-by: Isaac <no-reply@databricks.com>

*Why*
Multi-source review of the opt-out telemetry raised: the event over-counted
when the setting was already manual; the command-handler glue was untested; and
two type names collided / broke the repo's OptOut casing.
*What*
- Record the opt-out only on a genuine auto->manual transition (not on every
 successful write), so repeat invocations while already manual don't inflate
 the count. Extract the handler into optOutOfAutomatedPythonSetup with injected
 deps, covered by unit tests (transition, already-manual, no-folder, write
 failure).
- Rename the reported-flow type PythonEnvSetupMode -> ReportedSetupMode to avoid
 collision with PythonEnvironmentSetupMode / PythonSetupMode.
- Rename Optout -> OptOut in identifiers to match the repo's optOutOfInstallPrompt.
- Clarify the setupMode field comment: emitted per (trigger, project); measure
 prevalence by distinct user, not raw event share.
- Use import type for the now type-only telemetry imports.
*Verification*
- yarn build (tsc) and yarn test:lint clean; yarn test:unit green (1065 passing).
Co-authored-by: Isaac <no-reply@databricks.com>

The helper injects out the VS Code UI globals (window/workspace/commands) but
still imports the ConfigurationTarget enum as a runtime value, so its tests run
under the extension-host harness. Reword the doc-comment that claimed 'without
VS Code globals'.
Co-authored-by: Isaac <no-reply@databricks.com>