Allow explicit owned Wayland connections for deferred startup

[thanosapollo]

Dependency prerequisite for eval-exec/neomacs#454.

Deferred GUI attachment needs an explicit Wayland connection without changing process-wide display environment variables. Landing this change in the project fork also lets Neomacs stop depending on a personal fork.

Adds WaylandConnection and with_wayland_connection, creating a native event queue on the owned connection. Failed explicit initialization can retry; main-thread checks and the permanent successful-creation guard remain unchanged. Existing environment-based one-shot failure behavior is preserved. No new dependencies or vendoring.

This targets patch, the branch used by Neomacs. It adds one commit over 2290f91c602f8efdf102972457a25e8b6e36f90c: five files, +190/-5. NEOMACS_FORK.md names master, but targeting that branch would include six inherited X11/Windows commits outside this change.

Verification

• Focused Wayland-only and default-feature tests: 3 passed, 1 opt-in ignored in each configuration.
• Independent exact-tree correctness and maintainer-fit review: PASS / merge-worthy; 26 isolated native-compositor cases passed, including owned-connection lifetime, concurrent construction, failed-initialization retry and backend selection.
• Clippy, X11-only check and scoped stable rustfmt passed. Documentation built with one existing activation-token link warning.
• The contributor also reports human testing. This is runtime testing, not a claim of human code review.

Automated execution results are retained evidence for this unchanged reviewed tree, not new runs at submission. Nightly formatting, the full suite, MSRV, other targets and hosted CI remain unverified.

After acceptance into a project-owned ref, Neomacs can pin this fork's exact accepted revision. This dependency contribution does not itself close Neomacs rust-windowing#434.

An automated agent prepared and submitted this change; independent code review was also performed by an automated agent.

• Tested on all platforms changed
• Added a changelog entry
• Documented the new platform-specific API
• Added an example program

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