feat(cuda): use VPMM v3.1

[gaxiom]

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[Copilot]

Pull Request Overview

This PR upgrades the CUDA backend dependencies from stark-backend v1.2.1-rc.6 to v1.2.1-rc.7 and adjusts the async concurrency test configuration. The workspace version is bumped to 1.4.1-rc.3 to reflect these changes.

• Updated five stark-backend dependencies to v1.2.1-rc.7
• Reduced MAX_CONCURRENCY from 14 to 5 in the async concurrency test
• Bumped workspace version to 1.4.1-rc.3

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 and stark-backend dependencies to v1.2.1-rc.7
.github/workflows/base-tests.cuda.yml	Reduced MAX_CONCURRENCY parameter from 14 to 5 in async test

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[github-actions]

group	app.proof_time_ms	app.cycles	app.cells_used	leaf.proof_time_ms	leaf.cycles	leaf.cells_used
verify_fibair	(-7 [-3.0%]) 228	322,610	2,058,654	-	-	-
fibonacci	(+15 [+1.5%]) 993	1,500,209	2,100,402	-	-	-
regex	(-17 [-0.7%]) 2,343	4,137,502	17,695,216	-	-	-
ecrecover	(+2 [+0.3%]) 719	122,859	2,262,718	-	-	-
pairing	(+54 [+3.8%]) 1,463	1,745,742	25,468,210	-	-	-

Commit: e7d3104

Benchmark Workflow