chore: set cpp project version to 1.3.0 for release

[DanielKow]

What

Bumps cpp/CMakeLists.txt → project(zerobuffer VERSION 1.3.0) (was 1.1.0).

Why

Prep for the v1.3.0 release. The in-tree CMake version has drifted badly — it still said 1.1.0 while the latest tag is v1.2.8. Since find_package(zerobuffer CONFIG …) reports PROJECT_VERSION to consumers (and it feeds CPack for any future packaging), a released 1.3.0 that self-reports 1.1.0 would be misleading and would break any consumer that later adds a version constraint.

Context

v1.3.0 is the first release to contain the LatestFrame API, which is currently master-only and unreleased:

commit
0d795e2	feat: LatestFrameWriter/LatestFrameReader (producer-owned latest-frame, seqlock)
7ce680e	fix: open LatestFrameReader segment read-only so lower-privilege consumers can attach
d4bd402	fix: base LatestFrameReader liveness on segment magic (namespace-safe)

The latest tag v1.2.8 (2025-10-15) does not contain latest_frame at all, so no released version currently satisfies consumers like native-player.

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