fix: dispose orphaned progress notifications on language server shutdown

[MOHAMMED WASIM KHAN (wasim-builds)]

Fixes #16750

When a language server crashed or was restarted, any active progress notifications (started via python/beginProgress) would remain orphaned in the UI because the progressDeferred promise was never resolved during dispose().

This PR ensures that if the ProgressReporting instance is disposed, any pending progress deferred is resolved, closing the orphaned UI notification.

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[Bill Schnurr (bschnurr)]

🔒 Automated review in progress — Bill Schnurr (@bschnurr) is auto-reviewing this PR.

[Bill Schnurr (bschnurr)]

Verification: The relevant tests could not be fully run in the isolated environment; this review is not fully verified.

Result: could-not-verify

Summary: Verification could not run because no trusted sandbox image is configured for `microsoft/vscode-python`. The PR adds no tests, and existing tests do not reference `ProgressReporting` or its progress notifications. The new disposal behavior therefore remains unverified and uncovered.

Test runs: 1 not run

• ⚠️ Not run | Verification preflight and PR diff discovery | printf 'AUTOMATION_SANDBOX_PROFILE=%s\n' "${AUTOMATION_SANDBOX_PROFILE:-}"; git status --short; git diff --name-status upstream/main...HEAD; git diff --stat upstream/main...HEAD; if [ -d node_modules ]; then printf 'node_modules=present\n'; else printf 'node_modules=missing\n'; fi; if [ -d out ]; then printf 'out=present\n'; else printf 'out=missing\n'; fi; git diff --unified=20 upstream/main...HEAD

⚠️ Verification preflight and PR diff discovery diagnostic output

Container verification could not start: no trusted sandbox image is configured for microsoft/vscode-python, and local execution was not authorized.

[Bill Schnurr (bschnurr)]

Approved via Review Center.