feat: version qbench machine output

[tiye]

Summary

• add RFC 0103 for versioned qbench machine output
• emit stable schema and crate version fields in JSON and text modes
• preserve existing timing fields and total-nanosecond semantics

Validation

• make check
• git diff --check

This PR is stacked on PR #44 and should remain unmerged with the rest of the chain.

[Copilot]

Pull request overview

Adds a versioned, machine-readable schema marker to qbench output, ensuring consumers can reliably detect the output contract and crate version across JSON and text modes.

Changes:

• Introduces RFC 0103 defining qbench output schema + version fields and their stability rules.
• Updates qbench to emit schema=quickcoffee.qbench.v1 and the crate version in both JSON and text outputs.
• Extends CLI integration tests to validate presence of the new fields (with a recommendation to strengthen per-line checks for text output).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/cli_tools.rs	Updates integration test expectations to include schema and version for qbench output.
src/bin/qbench.rs	Adds schema/version emission to both JSON and text output formats.
RFCs/0103-qbench-schema-version.md	New RFC specifying the versioned qbench machine output contract.
RFCs/0000-project-scope.md	Updates the documented RFC coverage range to include RFC 0103.
README.md	Updates the README’s “implemented RFCs” reference to point to RFC 0103.

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