fix: Use new image_transport API when applicable

[bjsowa]

Public API Changes
None

Description
This fixes the build on rolling which recently removed the old API entirely.

The CI fails due to clang-tidy errors which I'll fix in another PR

[Copilot]

Pull request overview

Updates web_video_server to compile against newer ROS 2 (rolling) by switching QoS handling to rclcpp::QoS and conditionally using the newer image_transport API where required.

Changes:

• Replace rmw_qos_profile_t-based QoS selection with rclcpp::QoS (get_qos_profile_from_name).
• Update streamers to use the new QoS type and, for image_transport, select the correct API via a compile definition.
• Add a CMake version gate to define IMAGE_TRANSPORT_USES_OLD_API for older image_transport versions.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/utils.cpp	Switch QoS helper implementation to construct/return rclcpp::QoS.
include/web_video_server/utils.hpp	Update QoS helper declaration to return std::optional<rclcpp::QoS>.
src/streamers/ros_compressed_streamer.cpp	Adapt compressed-image subscriber QoS creation to the new QoS type.
src/streamers/image_transport_streamer.cpp	Use old vs. new image_transport API signatures conditionally and pass QoS appropriately.
CMakeLists.txt	Gate old/new image_transport API usage via image_transport_VERSION.

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