telemetry: track exception kinds

## Problem

Elevated levels of some exception types may indicate Toolkit or service problems. Currently, Toolkit telemetry doesn't indicate the *kind* of an exception.

## Proposal

1. For various kinds of exceptions, such as "rate limiting", set a flag/enum on the metric object indicating the exception kind, e.g. `result.exceptionType = rateLimited`.
2. As always, do not capture exception details (such as stacktrace or other strings). Only the exception kind.

Start by locating the telemetry metric object and the exception-handling entry points in the Toolkit. Identify the supported exception kinds, then define completion as recording only a kind flag or enum, such as rate limiting, without capturing stack traces or other exception details.

Written by the indexing model from the issue text.