Add IM\Recent service for im.recent.* support

[mesilov]

Problem

The Bitrix24 REST API methods im.recent.* (recent chats list, pinning, read/unread) are not yet supported by the SDK. See https://apidocs.bitrix24.com/api-reference/chats/index.html.

Proposed solution

Add a new service src/Services/IM/Recent/Service/Recent.php that wraps the following REST methods, following patterns in other src/Services/<Scope>/ folders. Scope: im.

Methods to implement

• im.recent.get — list the user's recent chats
• im.recent.hide — hide a dialog from the list
• im.recent.list — list recent dialogs with pagination
• im.recent.pin — pin/unpin a dialog
• im.recent.unread — toggle the "read" mark on a chat

Acceptance criteria

• Bitrix24\SDK\Services\IM\Recent\Service\Recent implements each method with correct parameter mapping and #[ApiEndpointMetadata] / #[ApiServiceMetadata(new Scope(['im']))] attributes
• IMServiceBuilder::recent() exposes the new service
• RecentItemResult with @property-read annotations covers all fields returned by im.recent.list / im.recent.get
• Unit tests in tests/Unit/Services/IM/Recent/Service/RecentTest.php pass (make test-unit)
• Integration tests in tests/Integration/Services/IM/Recent/Service/RecentTest.php pass
• tests/Integration/Services/IM/Recent/Result/RecentItemResultTest.php passes (annotation completeness + type-cast checks)
• make test-integration-im-recent target added to Makefile and a suite added to phpunit.xml.dist
• CHANGELOG.md entry under ## 3.2.0 – UNRELEASED → ### Added with link to this issue

Part of #422.