! Benchmark multiline strings

Build with the following command:
```bash
hadrian/build -j9 --freeze1
```
Then
```
GHC=/path/to/repo/_build/stage1/bin/ghc ./run.py
```

Note: `--flavour=perf` and `--flavour=bench` weren't working for me on my M2 Mac.
Errors about `StgWord` being `unsigned long long` or "build rule finished but
rts-something.dylib not built"

benchmark_multiline_strings.py

#!/usr/bin/env python3

from __future__ import annotations

import os
import string
import subprocess
import timeit
from pathlib import Path

HERE = Path(__file__).resolve().parent
GHC = Path(os.environ["GHC"])

NUM_ITERATIONS = 30

def show_str(s: str, *, escape: bool = True) -> str:
    if escape:
        s = s.replace("\\", "\\\\").replace('"', '\\"')
    return '"' + s + '"'

def show_char(c: str, *, escape: bool = True) -> str:
    if escape:
        c = c.replace("\\", "\\\\").replace("'", "\\'")
    return "'" + c + "'"

VALID_CHARS = string.ascii_letters + string.digits + string.punctuation + " "
STR = VALID_CHARS
ESCAPE_CHARS = [
    "\\\\",
    "\\a",
    "\\b",
    "\\f",
    "\\n",
    "\\r",
    "\\t",
    "\\v",
    "\\\\",
    '\\"',
    "\\'",
    "\\NUL",
    "\\SOH",
    "\\STX",
    "\\ETX",
    "\\EOT",
    "\\ENQ",
    "\\ACK",
    "\\BEL",
    "\\BS",
    "\\HT",
    "\\LF",
    "\\VT",
    "\\FF",
    "\\CR",
    "\\SO",
    "\\SI",
    "\\DLE",
    "\\DC1",
    "\\DC2",
    "\\DC3",
    "\\DC4",
    "\\NAK",
    "\\SYN",
    "\\ETB",
    "\\CAN",
    "\\EM",
    "\\SUB",
    "\\ESC",
    "\\FS",
    "\\GS",
    "\\RS",
    "\\US",
    "\\SP",
    "\\DEL",
    "\\xa8bd",
    "\\o111",
    "\\189",
]

class Bench:
    def get_vals(self) -> list[str]:
        raise NotImplemented

    def run(self):
        name = self.__class__.__name__

        testdir = HERE / name
        testdir.mkdir(parents=True, exist_ok=True)

        program = "main = {}".format(
            " >> ".join(
                f'print {s}'
                for s in self.get_vals()
            )
        )

        input_file = testdir / "input.hs"
        input_file.write_text(program)

        def compile():
            p = subprocess.run(
                [GHC, input_file],
                capture_output=True,
                cwd=testdir,
            )
            if p.returncode != 0:
                stderr = p.stderr.decode()
                n = 1000
                raise Exception(stderr[:n] + "[...]" + stderr[-n:])

        print(f"=====> {name}")
        duration = timeit.timeit(compile, number=NUM_ITERATIONS)
        print(f"Average: {duration / NUM_ITERATIONS} secs")
        print("")

class BenchLongString(Bench):
    def get_vals(self) -> list[str]:
        return [show_str(STR * 10000)]

class BenchManyStrings(Bench):
    def get_vals(self) -> list[str]:
        return [show_str(STR) for _ in range(10000)]

class BenchLongEscapeString(Bench):
    def get_vals(self) -> list[str]:
        return [show_str("".join(ESCAPE_CHARS) * 1000, escape=False)]

class BenchManyChars(Bench):
    def get_vals(self) -> list[str]:
        return [show_char(c) for c in VALID_CHARS] * 100

class BenchManyEscapeChars(Bench):
    def get_vals(self) -> list[str]:
        return [show_char(c, escape=False) for c in ESCAPE_CHARS] * 1000

if __name__ == "__main__":
    print(f"Running benchmarks against: {GHC}")
    print("")

    BenchLongString().run()
    BenchManyStrings().run()
    BenchLongEscapeString().run()
    BenchManyChars().run()
    BenchManyEscapeChars().run()

result_master.log

Running benchmarks against: /Users/bchinn/repos/ghc/_build/stage1/bin/ghc

=====> BenchLongString
Average: 0.091564694433085 secs

=====> BenchManyStrings
Average: 0.09195360000012442 secs

=====> BenchLongEscapeString
Average: 0.09198539306526073 secs

=====> BenchManyChars
Average: 0.09180612780037337 secs

=====> BenchManyEscapeChars
Average: 0.09192637363254713 secs

result_multiline.log

Running benchmarks against: /Users/bchinn/repos/ghc/_build/stage1/bin/ghc

=====> BenchLongString
Average: 0.09138900000058735 secs

=====> BenchManyStrings
Average: 0.09150341526643994 secs

=====> BenchLongEscapeString
Average: 0.09167130139928001 secs

=====> BenchManyChars
Average: 0.09189670833487375 secs

=====> BenchManyEscapeChars
Average: 0.09206391806559017 secs