Fix Posthog by correctly copying .env in the build process

[cte]

Description

I also noticed that the part of the CI action that validates the package doesn't seem to be working:

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Important

Fixes build process by correctly copying optional .env file and updates CI workflow to prevent broken pipe issues.

• Build Process:
  • Fixes .env file copying in apps/vscode-nightly/esbuild.mjs and src/esbuild.mjs by marking it as optional in copyPaths.
  • Updates copyPaths function in packages/build/src/esbuild.ts to handle optional files.
• CI Workflow:
  • Modifies marketplace-publish.yml to save VSIX contents to a temporary file to avoid broken pipe issues.
  • Ensures .env file is included in package validation in marketplace-publish.yml.
• Miscellaneous:
  • Removes .prettierignore and adds ignore paths to .prettierrc.json.

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