Add devMode setting to prevent rate limiting during development

[Copilot]

Implementation Plan for Dev Mode Setting

• Add devMode configuration setting to package.json
• Add localization string for devMode setting in package.nls.json
• Add devMode constant to settingKeys.ts
• Implement devMode check in copilotPrWatcher.ts to skip automatic polling
• Implement devMode check in prsTreeModel.ts to skip Copilot PR status fetching
• Implement devMode check in categoryNode.ts to collapse all PR queries by default
• Implement devMode check in stateManager.ts at initialization (moved from setIssueData)
• Run linting and hygiene checks
• Run code review (no issues found)
• Run CodeQL security scan (no alerts found)

Summary

Successfully implemented the githubPullRequests.devMode setting as requested in the issue. When enabled, this setting:

1. Disables automatic Copilot PR status polling - Stops the timer-based polling in copilotPrWatcher.ts that runs every 2-5 minutes
2. Skips Copilot PR status fetching - Prevents expensive timeline event queries in prsTreeModel.ts
3. Collapses all PR query categories - All PR queries start collapsed in the tree view
4. Disables issues fetching - Checks dev mode once at initialization in doInitialize method rather than per-folder in setIssueData

This helps extension developers avoid hitting rate limits during frequent reloads while working on the extension. The setting defaults to false so normal users are unaffected.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add a "dev mode" setting</issue_title>
<issue_description>When I'm working on the extension, I might reload dozens of times in an hour. This can cause me to blow through my rate limit. We should have a githubPullRequests.devMode setting, which limits some of the more expensive API calls that can become problematic:

• Don't Copilot PR status automatically and on a timer
• Collapse all PR queries
• Don't fetch issues</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add a "dev mode" setting #8303

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[alexr00]

@copilot Do the dev mode check here, not in set issue data.

[Copilot]

Done in b6694ef. Moved the dev mode check to doInitialize() where it checks once at initialization time instead of in each setIssueData() call.