bin: remove realpath, use testing env instead

If env.__TESTING_RIMRAF_BIN__=='1', then just export. Otherwise,
do the thing. This saves a realpath call at startup in the bin.

src/bin.mts

@@ -1,5 +1,4 @@
 #!/usr/bin/env node
-import { realpathSync } from 'fs'
 import { readFile } from 'fs/promises'
 import type { RimrafAsyncOptions } from './index.js'
 import { rimraf } from './index.js'
@@ -262,11 +261,7 @@ main.help = help
 
 export default main
 
-const isMainModule =
-  realpathSync(String(process.argv[1])) ===
-  realpathSync(fileURLToPath(import.meta.url))
-
-if (isMainModule) {
+if (process.env.__TESTING_RIMRAF_BIN__ !== '1') {
   const args = process.argv.slice(2)
   main(...args).then(
     code => process.exit(code),

test/bin.ts

@@ -10,9 +10,11 @@ t.test('basic arg parsing stuff', async t => {
   const LOGS: any[] = []
   const ERRS: any[] = []
   const { log: consoleLog, error: consoleError } = console
+  process.env.__TESTING_RIMRAF_BIN__ = '1'
   t.teardown(() => {
     console.log = consoleLog
     console.error = consoleError
+    delete process.env.__TESTING_RIMRAF_BIN__
   })
   console.log = (...msg) => LOGS.push(msg)
   console.error = (...msg) => ERRS.push(msg)