fix: add marker windows stubs

[not-matthias]

• Fixed the return types in the header (zig exports it as u8)
• Added the missing marker functions

[Copilot]

Pull Request Overview

Adds Windows stubs for marker/timestamp APIs and updates the example to demonstrate start/end benchmark markers around a function call.

• Add instrument_hooks_current_timestamp and instrument_hooks_add_marker stubs on Windows.
• Update example to record start/end timestamps around example_function and include an artificial expensive setup step.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
scripts/windows_stub.c	Adds Windows stub implementations for timestamp and marker APIs.
example/main.c	Demonstrates capturing timestamps and adding benchmark start/end markers; introduces helper functions for workload.

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[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

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