[Repo Assist] perf: reuse stable temp file per document to reduce filesystem overhead

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🤖 This is an automated PR from Repo Assist.

Problem

format() generates a fresh random temp file name on every save:

let fileName = TmpDir + "/temp-" + Math.random().toString(36)…+ ".php";
fs.writeFileSync(fileName, text);
// …phpcbf runs…
fs.unlink(fileName, function(err) {});

This means every save causes:

1. A Math.random() call + several string operations to build the name
2. A new filesystem inode allocation for the new file
3. An async unlink (inode deletion) after each run

For users who save frequently (e.g. on every keystroke via editor.formatOnSave), this creates constant inode churn in the OS temp directory.

Fix

Allocate one stable temp file path per document (keyed by document.uri.toString()) on first use, and overwrite it in-place on subsequent saves. Temp file names are now phpcbf-(pid)-(n).php, scoped to the running process for easy identification.

Lifecycle:

• Temp file is created lazily on the first format() call for a document
• Cleaned up in onDidCloseTextDocument when the user closes the tab
• All remaining temp files are removed synchronously in deactivate()

Trade-offs

• Slightly more memory (one Map entry + one file on disk per open PHP document); negligible in practice
• If VS Code crashes without calling deactivate(), a small number of temp files persist — same as the previous code, and the OS temp cleaner handles these

Test Status

Unit tests (node --test test/unit.test.js): 7/7 passing ✅
Syntax check (node --check extension.js): OK ✅
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