Add parser performance benchmarks with CI comparison workflow

[Copilot]

Restores performance testing for the parser using the ordo-one/package-benchmark framework, previously removed in #100.

Changes

• Benchmark implementation: Two benchmarks using the existing 6.5k line Big.beancount test file

  • Parse Big File: Measures file I/O + parsing via Parser.parse(contentOf:)
  • Parse Big File (String): Measures pure parsing via Parser.parse(string:) with pre-loaded content

• CI workflow: Runs on PRs, benchmarks base vs head in same runner, posts markdown comparison to PR, fails on >10% regression

• Dependencies: Added package-benchmark 1.29.7+, includes jemalloc for memory profiling

let benchmarks = {
    let config = Benchmark.Configuration(
        metrics: [.wallClock, .throughput],
        scalingFactor: .kilo,
        maxDuration: .seconds(10)
    )

    Benchmark("Parse Big File", configuration: config) { benchmark in
        let fileURL = loadBigFile()
        benchmark.startMeasurement()
        for _ in benchmark.scaledIterations {
            _ = try Parser.parse(contentOf: fileURL)
        }
    }
}

Workflow follows the official CI comparison guide for baseline comparison in the same runner environment.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https /usr/lib/apt/methods/https -parse-as-library -incremental -c @/home/REDACTED/work/SwiftBeanCount/SwiftBeanCount/.build/x86_64-REDACTED-linux-gnu/debug/SwiftBeanCountParser.build/sources -I /home/REDACTED/work/SwiftBeanCount/SwiftBeanCount/.build/x86_64-REDACTED-linux-gnu/debug/Modules rk/Sources/Benchmark/ARCStats/ARCStats.swift x86_64-REDACTED-linux-gnu rk/Sources/Benchmark/ARCStats/ARCStatsProducer.swift -enable-batch-mode rk/Sources/Benchmark/Benchmark+ConvenienceInitializers.swift -e rk/Sources/Benchmark/Benchmark.swift git rk/Sources/Benchmark/BenchmarkClock.swift l rk/Sources/Benchmark/BenchmarkExecutor+Extensions.swift 917bb95775729d4f-emit-module rk/Sources/Benchmark/BenchmarkExecutor.swift (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Parser performance tests</issue_title>
<issue_description>The parser had an attempt at performance tests, which were removed in #100
We should bring them back, using https://www.swift.org/blog/benchmarks/

for this we should follow https://swiftpackageindex.com/ordo-one/package-benchmark/1.29.7/documentation/benchmark/comparingbenchmarksci and probably use CI to run the base and head branch of a PR after each other in the same runner (but different action from the testing) to compare and fail at a certain threshold.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Parser performance tests #15

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