task implement SUBSCRIBE and UNSUBSCRIBE commands with corresponding …

[Aravinda-HWK]

📌 Description

This PR is used to implement the "SUBSCRIBE" command and write the test cases for that command.

• Closes [TASK] Implement "SUBSCRIBE" command and write the test cases #39

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🔍 Changes Made

1. Write the test cases for "SUBSCRIBE", "UNSUBSCRIBE", and "LSUB" commands
2. Implement the above commands first.

✅ Checklist (Email System)

• Core IMAP commands tested (LOGIN, CAPABILITY, LIST, SELECT, FETCH, LOGOUT).
• Authentication is tested.
• Docker build & run validated.
• Configuration loading verified for default and custom paths.
• Persistent storage with Docker volume verified.
• Error handling and logging verified
• Documentation updated (README, config samples).

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🧪 Testing Instructions

To test the server, use the instructions in the README in the test directory.

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📷 Screenshots / Logs (if applicable)

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⚠️ Notes for Reviewers

[Copilot]

Pull Request Overview

This PR implements the SUBSCRIBE, UNSUBSCRIBE, and LSUB commands for the IMAP server with comprehensive test coverage. It adds subscription functionality that allows users to subscribe to mailboxes and list their subscribed mailboxes.

• Implements SUBSCRIBE and UNSUBSCRIBE command handlers with proper authentication and validation
• Adds LSUB command to list subscribed mailboxes, replacing hardcoded behavior with database-backed subscriptions
• Creates comprehensive test suite covering various scenarios including edge cases and error conditions

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/server/subscribe_test.go	Comprehensive test suite for SUBSCRIBE, UNSUBSCRIBE, and LSUB commands with 12 test cases
test/helpers/test_helpers.go	Adds subscriptions table creation to test database setup
internal/server/testing.go	Exposes subscription-related handlers for testing
internal/server/handlers.go	Implements SUBSCRIBE, UNSUBSCRIBE handlers and updates LSUB to use database subscriptions
internal/server/connection.go	Adds routing for SUBSCRIBE and UNSUBSCRIBE commands
internal/db/sqlite.go	Adds database functions for subscription management
Makefile	Adds test targets for subscription commands
.github/workflows/ci.yml	Adds CI test steps for subscription commands

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