ci: disable unused coverage instrumentation

[bernalde]

Summary

• disable unused coverage instrumentation across the full DWave Julia/OS matrix
• retain every backend, parity, topology, and QUBODrivers test on every existing matrix leg
• remove stale commented coverage/upload configuration

Validation

• actionlint
• git diff --check
• full Julia 1.10/current × Ubuntu/Windows CI matrix (post-push)

Measurement

Issue #67 recorded 34.6 aggregate runner-minutes. Current-Julia test logs showed 92 dependencies precompiled under coverage in 166 seconds on Ubuntu and 217 seconds on Windows.

• attempt 1: 32.5 aggregate runner-minutes; longest job 11m07s
• warm rerun: 29.6 aggregate runner-minutes; longest job 10m06s
• sampled CI logs show coverage=false; both complete four-job matrices passed with every backend and interface test retained

The warm rerun used 2.9 fewer aggregate runner-minutes than attempt 1 and 5.0 fewer than the audited baseline. These timings still include material runner/cache variance, so the reliable change is removal of unused coverage work from all four jobs.

Branch Hygiene

• Base: main at 0d4d024046b0cde8e9b4895d41e074be24fa7d96
• Not stacked; open PR Make compatibility checks Dependabot-safe #66 changes test/compat_metadata.jl, not the workflow changed here.

Closes #67