feat: implement NOOP command handling and state tracking

[Aravinda-HWK]

📌 Description

This PR is for implementing the "NOOP" command and the test cases for test it.

• Closes [TASK] Implement the "NOOP" command #6

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🔍 Changes Made

• Added handleNoop function to manage NOOP command responses based on client state.

• Updated ClientState struct to track last message and recent counts.

• Enhanced CI workflow to include specific tests for the NOOP command.

• Created comprehensive tests for NOOP command scenarios, including authenticated and unauthenticated states.

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✅ 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

You can read the README.md file in the test folder to run the test files.

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📷 Screenshots / Logs (if applicable)

N/A

⚠️ Notes for Reviewers

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[Copilot]

Pull Request Overview

This PR implements the NOOP command handling and state tracking for an IMAP server implementation, allowing clients to check for mailbox updates and maintain connection activity.

• Adds complete NOOP command handler with proper RFC 3501 compliance
• Introduces mailbox state tracking fields to monitor message counts and recent messages
• Creates comprehensive test suite covering all NOOP command scenarios and edge cases

Reviewed Changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/server/noop_test.go	Comprehensive test suite for NOOP command with 355 lines covering authentication states, response formats, concurrency, and RFC compliance
internal/server/testing.go	Exposes HandleNoop method for testing
internal/server/handlers.go	Implements complete handleNoop function with mailbox state checking and untagged response generation
internal/server/fetch.go	Initializes state tracking fields during SELECT command
internal/server/connection.go	Updates NOOP command routing to use new handler instead of simple response
internal/models/state.go	Adds LastMessageCount and LastRecentCount fields to ClientState struct
Makefile	Adds NOOP-specific test targets and improves help documentation
.github/workflows/ci.yml	Updates CI workflow to include NOOP command tests

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