Avoid Linux precompile hangs in live workload

[quinnj]

Summary

• use Base.timedwait for the HTTP precompile workload watchdog instead of Reseau.IOPoll.timedwait
• make the live server/request precompile workload opt-in on Linux with Julia 1.11+
• add Preferences as a direct dependency since HTTP now reads its own precompile_workload preference

Context

Issue #1252 is still reproducible for affected Linux users even with Reseau@1.1.4. The issue history points at the live HTTP precompile workload: precompile_workload=false avoids the hang, and the reports are on Linux Julia 1.11/1.12 while Julia 1.10 eventually completes.

This keeps the workload enabled by default for macOS/Windows and Linux Julia 1.10, but avoids running live local servers/requests during precompile for the Linux Julia 1.11+ lane where users are hanging. Users can still explicitly opt in with precompile_workload=true.

Testing

• julia --project=. -e 'using HTTP; HTTP._run_precompile_workload!(); println("precompile workload ok")'
• julia +1.10.11 --startup-file=no -e 'using Pkg; tmp = mktempdir(); Pkg.activate(tmp); Pkg.develop(path="/tmp/http-1252-fix"); Pkg.precompile(); using HTTP; @show VERSION; @show HTTP._precompile_workload_enabled(); @show Base.timedwait(() -> true, 1.0; pollint=0.01)'
• docker run --rm --platform linux/arm64 -v /tmp/http-1252-fix:/work -e JULIA_DEPOT_PATH=/tmp/julia-depot-arm julia:1.12.6 --startup-file=no -e 'using Pkg; Pkg.activate(temp=true); Pkg.develop(path="/work"); Pkg.precompile(); using HTTP; @show Sys.islinux(); @show VERSION; @show HTTP._precompile_workload_enabled()'
• julia --project=. -e 'using Pkg; Pkg.test()'

Co-authored by Codex

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.91%. Comparing base (62e7d69) to head (7e80f0e).

Files with missing lines	Patch %	Lines
src/precompile.jl	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1274      +/-   ##
==========================================
+ Coverage   84.88%   84.91%   +0.03%     
==========================================
  Files          28       28              
  Lines       10711    10713       +2     
==========================================
+ Hits         9092     9097       +5     
+ Misses       1619     1616       -3     

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[quinnj]

Closing this. The workaround shape here is not the right answer for issue #1252; we need to continue root-cause investigation instead of disabling the workload.