Stream workspace metadata JSON serialization

[zaniebot]

uv workspace metadata currently serializes the entire pretty-printed response into a String before writing it, adding a full-response allocation for large workspaces. Serialize directly into a buffered, locked standard-output stream instead, while preserving the existing JSON formatting and output suppression behavior.

On Namespace, I measured uv workspace metadata --offline --frozen with optimized profiling builds and stdout redirected to /dev/null. Each version was measured in 41 interleaved rounds after warmups. Values are means; changes are relative to main, with paired-bootstrap 95% confidence intervals from 20,000 resamples.

Wall time (ms):

Workspace	Packages	JSON	main	This change	Change (95% CI)
Small: uv	77	0.46 MB	30.82	29.02	−5.8% [−15.7%, +4.6%]
Medium: Prefect	363	2.01 MB	40.05	38.87	−3.0% [−11.5%, +6.5%]
Large: synthetic	6,346	20.53 MB	313.10	300.21	−4.1% [−7.2%, +0.5%]
Large: synthetic + environment	6,346	26.80 MB	425.68	403.18	−5.3% [−6.3%, −4.2%]

Peak RSS (MiB):

Workspace	main	This change	Change (95% CI)
Small: uv	34.67	34.50	−0.5% [−1.4%, +0.4%]
Medium: Prefect	43.55	41.66	−4.3% [−5.2%, −3.6%]
Large: synthetic	150.64	115.38	−23.4% [−23.8%, −23.0%]
Large: synthetic + environment	164.83	132.34	−19.7% [−19.9%, −19.5%]

The small and medium cases use real public uv and Prefect lockfiles. The synthetic workspace has 4,864 members, 10,242 resolution nodes, and 79,264 dependency edges.

[astral-automations-bot]

Promoted to #20990.