Add AIC to agent debug panel

[pwang347]

Fixes #314417
CC @vijayupadya

[Copilot]

Pull request overview

This PR plumbs Copilot per-request usage credits (from copilot_usage.total_nano_aiu) through the chat debug event pipeline and surfaces an aggregated “Copilot Usage (AIC)” metric in the Agent Debug Logs overview.

Changes:

• Extend chat debug “model turn” events (proposed API + internal DTOs) with copilotUsageNanoAiu.
• Emit and persist the copilot_usage.total_nano_aiu value from Copilot OTel spans/debug logs into chat debug model turn events.
• Display total Copilot usage (converted to AIC) in the Chat Debug Overview “Summary” metrics.

Show a summary per file

File	Description
src/vscode-dts/vscode.proposed.chatDebug.d.ts	Adds copilotUsageNanoAiu to the proposed ChatDebugModelTurnEvent API surface.
src/vs/workbench/contrib/chat/common/chatDebugService.ts	Extends internal model-turn debug event type with copilotUsageNanoAiu.
src/vs/workbench/contrib/chat/browser/chatDebug/chatDebugOverviewView.ts	Aggregates nano-AIU usage and conditionally renders “Copilot Usage (AIC)” in the overview metrics.
src/vs/workbench/api/common/extHostTypes.ts	Adds copilotUsageNanoAiu to the extension-host type wrapper for model turn events.
src/vs/workbench/api/common/extHostChatDebug.ts	Serializes/deserializes copilotUsageNanoAiu between ext host objects and DTOs.
src/vs/workbench/api/common/extHost.protocol.ts	Extends the model-turn event DTO with copilotUsageNanoAiu.
src/vs/workbench/api/browser/mainThreadChatDebug.ts	Forwards copilotUsageNanoAiu through main-thread event serialization and revival.
extensions/copilot/src/platform/otel/common/genAiAttributes.ts	Introduces an OTel attribute key for copilot_usage.total_nano_aiu.
extensions/copilot/src/extension/trajectory/vscode-node/otelSpanToChatDebugEvent.ts	Maps the new OTel attribute into vscode.ChatDebugModelTurnEvent.copilotUsageNanoAiu.
extensions/copilot/src/extension/prompt/node/chatMLFetcher.ts	Attaches copilot_usage.total_nano_aiu onto inference spans as an attribute.
extensions/copilot/src/extension/chat/vscode-node/chatDebugFileLoggerService.ts	Includes copilotUsageNanoAiu when logging spans to the debug log file format.

Copilot's findings

• Files reviewed: 10/11 changed files
• Comments generated: 1