Baseline workflow profiling and bottleneck analysis (EPIC #1840)

[josecelano]

Parent EPIC: #1840

Goal

Measure where time is spent in .github/workflows/container.yaml and .github/workflows/testing.yaml, then record a baseline that can be reused to compare future workflow optimizations.

Scope highlights

• cold/no-cache and warm-cache measurements for both workflows
• workflow phase-level bottleneck visibility
• linker-heavy target analysis for container build path
• durable benchmark artifact updated as later optimizations land

Acceptance highlights

• bottlenecks identified with concrete evidence
• reusable benchmark/report maintained in-repo
• procedure explicit enough for repeatable reruns

Spec draft currently tracked in repository under workflow-performance baseline subissue docs.