[flutter_tools] Remove AzureDetector IMDS probe from BotDetector #194405

AzureDetector.isRunningOnAzure probes the Azure Instance Metadata Service (http://169.254.169.254/metadata/instance) on startup and caches isRunningOnBot = true in ~/.flutter_tool_state, which classifies every Azure-hosted developer workstation as a CI bot and forces BotDetector.isRunningOnBot to be asynchronous.

• Root cause: BotDetector.isRunningOnBot falls back to an HTTP GET to 169.254.169.254 whenever no CI environment variable is set, treating any HTTP response (including HttpException at #L108-L111) as a bot and persisting that result in persistentToolState. Meanwhile, bot_detector.dart#L42 checks _platform.environment.containsKey('CI'), treating CI=false and CI=0 as bots.
• Impact: Human developers using GitHub Codespaces, Microsoft Dev Box, or Azure VMs are permanently flagged as bots—suppressing analytics (NoOpAnalytics()), skipping update checks (flutter_command_runner.dart#L477), and auto-deleting ~/.gradle without prompting on Gradle errors (gradle_errors.dart#L195)—while non-Azure users pay up to a 250ms–1s network timeout on first run or hit proxy redirect issues (see #189456). Azure Pipelines CI runs are already detected synchronously via TF_BUILD (bot_detector.dart#L69).

Proposed Fix

• Remove AzureDetector and the persistentToolState.isRunningOnBot cache from packages/flutter_tools/lib/src/base/bot_detector.dart, matching pkg/dartdev.
• Require CI in bot_detector.dart#L42 to be non-empty and not 'false' or '0' (and delegate to package:unified_analytics once centralized in dart-lang/tools#2672).