chore: update stark-backend to v1.2.3

[jonathanpwang]

No description provided.

[Copilot]

Pull request overview

This PR updates the stark-backend dependency from v1.2.2 to v1.2.3 and bumps the workspace version to 1.4.3-rc.0, bringing in fixes to metered execution and CUDA tracegen optimizations.

Changes:

• Updated stark-backend dependencies (openvm-stark-backend, openvm-stark-sdk, openvm-cuda-backend, openvm-cuda-builder, openvm-cuda-common) from v1.2.2 to v1.2.3
• Bumped workspace version from 1.4.2 to 1.4.3-rc.0
• Added v1.4.3 release notes to CHANGELOG.md

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
Cargo.toml	Updated workspace version to 1.4.3-rc.0 and stark-backend dependencies from v1.2.2 to v1.2.3
Cargo.lock	Reflected version updates for all workspace packages and stark-backend dependencies with new commit hashes
CHANGELOG.md	Added v1.4.3 release notes documenting prover fixes and CUDA optimizations

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[github-actions]

group	app.proof_time_ms	app.cycles	app.cells_used	leaf.proof_time_ms	leaf.cycles	leaf.cells_used
verify_fibair	(+10 [+4.5%]) 234	322,610	2,058,654	-	-	-
fibonacci	(-37 [-3.5%]) 1,012	1,500,209	2,100,402	-	-	-
regex	(-3 [-0.1%]) 2,299	4,137,502	17,695,216	-	-	-
ecrecover	(-25 [-3.3%]) 727	122,859	2,263,998	-	-	-
pairing	(+35 [+2.4%]) 1,469	1,745,742	25,408,302	-	-	-

Commit: 5d7c550

Benchmark Workflow