* Enhanced existing tests for the `resolveHeaders` function to cover all user field placeholders and messy scenarios.
* Added basic integration tests for custom endpoints initialization file
* 🔧 refactor: move `processMCPEnv` from `librechat-data-provider` and move to `@librechat/api`
* 🔧 refactor: Update resolveHeaders import paths
* 🔧 refactor: Enhance resolveHeaders to support user and custom variables
- Updated resolveHeaders function to accept user and custom user variables for placeholder replacement.
- Modified header resolution in multiple client and controller files to utilize the enhanced resolveHeaders functionality.
- Added comprehensive tests for resolveHeaders to ensure correct processing of user and custom variables.
* 🔧 fix: Update user ID placeholder processing in env.ts
* 🔧 fix: Remove arguments passing this.user rather than req.user
- Updated multiple client and controller files to call resolveHeaders without the user parameter
* 🔧 refactor: Enhance processUserPlaceholders to be more readable / less nested
* 🔧 refactor: Update processUserPlaceholders to pass all tests in mpc.spec.ts and env.spec.ts
* chore: remove legacy ChatGPTClient
* chore: remove LLM initialization code
* chore: initial deprecation removal of `gptPlugins`
* chore: remove cohere-ai dependency from package.json and package-lock.json
* chore: update brace-expansion to version 2.0.2 and add license information
* chore: remove PluginsClient test file
* chore: remove legacy
* ci: remove deprecated sendMessage/getCompletion/chatCompletion tests
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Co-authored-by: Dustin Healy <54083382+dustinhealy@users.noreply.github.com>
