fix(run): start pipe drain before waitForProcess to avoid 64KB deadlock

[poolcamacho]

Closes #4.

Reported by @just-doit. Reproducible on any repo whose git log output exceeds the macOS pipe buffer (~64 KB).

Regression

When GitService.run was decomposed into helpers, the read tasks were moved inside drainAndClose, which run called only after waitForProcess returned:

let completed = await waitForProcess(process, timeout: timeout)  // <- blocks here
let (outData, errData) = await drainAndClose(...)                 // <- reads start here

While the process was alive, nothing was reading the pipes. Once the kernel pipe buffer filled (~64 KB), git blocked on write, process.isRunning stayed true, and the timeout eventually fired.

Fix

Split drainAndClose into:

• startDraining (synchronous, returns the two Task handles) — called right after process.run().
• awaitDrain (async, awaits the values and closes the read ends) — called after waitForProcess.

The detached read tasks now live for the whole lifetime of the child process, so the pipe buffer can't deadlock git regardless of output size.

Verification

• xcodebuild build clean
• swiftlint --strict clean
• Manual reproduction: opened a repo whose git log --all exceeds 64 KB on b0a0a02, confirmed the timeout. Re-tested on this branch, loads in normal time with no timeout.