Fix Windows CI EPERM error with retry logic

Problem

Windows CI runners fail intermittently with:

EPERM: operation not permitted, rename 
'C:\Users\RUNNER~1\AppData\Local\Temp\sls-ajvXXX\...' 
-> 'C:\Users\runneradmin\.serverless\artifacts\...'

This occurs even after fixing the temp directory location because Windows can throw EPERM transiently due to file handle timing issues.

Solution

Added EPERM retry logic in safe-move-file.js with exponential backoff:

• Retry 1: 100ms delay
• Retry 2: 200ms delay
• Retry 3: 400ms delay

Total max wait: 700ms before throwing.

Safety Analysis

Verified all 3 usages of safeMoveFile are safe for retry:

• resolve-ajv-validate.js: Content-addressed files (hash-based filenames)
• generate-zip.js: Deterministic zip from static source files
• log-deprecation.js: Idempotent text file write

Changes

• packages/serverless/lib/utils/fs/safe-move-file.js: Add EPERM retry with exponential backoff