stream Cargo JSON directly into BinaryList

[cornmander]

summary

• add a BinaryListBuilder that can consume Cargo messages incrementally, and reuse it from BinaryList::from_messages
• teach the cargo-nextest binary-list build path to process Cargo stdout in one pass instead of buffering it and reparsing it later
• add a regression test for the line-by-line parsing path

Closes #3129.

testing

• cargo xfmt
• cargo nextest run -p nextest-runner -p cargo-nextest

experimental findings

I benchmarked the warmed end-to-end CLI path that this change targets:

cargo-nextest nextest list --workspace --all-targets --list-type binaries-only \
  --cargo-message-format json --cargo-quiet >/dev/null

using hyperfine --warmup 5 --runs 20 on two external repositories:

• tokio (e67cd87): 426.3 ms ± 37.3 ms before, 400.6 ms ± 10.6 ms after, about 6.0% faster
• rust-analyzer (51966da): 426.4 ms ± 36.4 ms before, 400.6 ms ± 11.9 ms after, about 6.1% faster

These runs intentionally benchmark the Cargo-JSON-forwarding list path, since that is the path changed by this patch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.44%. Comparing base (9531cb9) to head (0df9104).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3131      +/-   ##
==========================================
+ Coverage   84.43%   84.44%   +0.01%     
==========================================
  Files         156      156              
  Lines       42733    42811      +78     
==========================================
+ Hits        36080    36153      +73     
- Misses       6653     6658       +5     

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[sunshowers]

Thank you! Just a few minor notes for myself that I'll fix in a followup.