ci: unblock CI via a uv constraint

[davidhewitt]

The 3.9 jobs are broken due to kislyuk/argcomplete#559

I think it's possible to use a uv constraint override to fix the nox install. To make this work I had to migrate existing pip installs of nox to use uvx nox instead.

[codspeed-hq]

Merging this PR will degrade performance by 20.33%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 1 regressed benchmark
✅ 139 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	into_u128_u64_max	3.6 µs	4.5 µs	-20.33%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing davidhewitt:uv-constraint (64096eb) with main (09228f6)}

[davidhewitt]

I will merge to keep things moving.