Add --session-name flag to record-trace

[utpilla]

Addresses #289 (comment)

Changes

Adds an optional --session-name <name> flag to record-trace that sets the ETW/perf session name used for recording. Defaults to "record-trace" when omitted, preserving current behavior.

Motivation

record-trace previously hardcoded the session name "record-trace". On Windows, after the GUID-from-name fix (#289), the session name determines the session's identity:

• A fixed name (the default) means one record-trace ETW session per machine at a time, but a new run automatically reclaims a session left behind by a crashed one.
• A unique name (e.g. per-PID) lets multiple record-trace ETW sessions run side by side.

On Linux the name has no such constraint. perf sessions are scoped per PID/CPU, so concurrent runs already work regardless of name. The flag is primarily a Windows concurrency control and reads as a harmless session label on Linux.

This flag lets users opt into concurrent recording on Windows when they need it, while keeping the safe singleton + crash-recovery default for the common case.

[beaubelgrave]

Thanks!