Deep-dive: ETW / -Z time-passes Allocator Profiling on Windows with Repro

[hyperpolymath]

Goal: Run a bespoke allocation/profiling deep-dive using ETW and -Z time-passes on the original file and toolchain as described in #38.

Tasks:

• Set up a stable-x86_64-pc-windows-msvc Windows 11 host with full native devtooling, matching the environment described in Residual #14: obtain exact ~330 LOC repro + Windows ETW/-Z time-passes deep-dive #38.
• If the original file is found (see sub-issue 'repro-file'), use that; otherwise document limitations using the closest available artefact.
• Collect allocation and timing profiles using ETW, -Z time-passes, heaptrack, and dhat.
• Compare metrics to current Linux/Windows-CI figures and produce a report.

Definition of Done:

• Profiling environment established with correct artefact.
• ETW, heaptrack, dhat, and -Z time-passes output attached.
• Comparative notes added on performance characteristics and differences.