feat(vscode): add diagnostics profiling

[hongjr03]

This adds a VS Code diagnostics profiling flow for Vizsla.

• add a Vizsla: Profile Diagnostics command for current-file and workspace diagnostics
• run a dedicated profiling language-server session with Chrome trace output enabled
• write profiling artifacts, including trace summary, folded stacks, static flamegraph, and raw trace JSON
• bundle Speedscope assets in the VSIX and open interactive profiles in the external browser
• keep large interactive trace rendering outside the VS Code webview process