docs: add ExactMatch score example

[Rul1an (Rul1an)]

What changed

Adds a small ExactMatch example to SCORERS.md showing the returned score object fields users usually inspect: name and score.

Why

The surrounding section already documents the binary 0 / 1 score range, but the concrete returned object shape was less visible than in nearby scorer examples.

Validation

Ran locally:

git diff --check

[Copilot]

Pull request overview

Adds a concrete ExactMatch usage snippet to the scorer docs to make the returned Score object shape (notably name and score) more discoverable alongside the existing binary score range description.

Changes:

• Add a Python example for ExactMatch demonstrating result.name and result.score.

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