fix(logs): use UnixMilli for v1 logs search timestamps

[ibrahimridene]

Summary

• parseTimeString returns milliseconds but runLogsSearch passed them to time.Unix() which expects seconds
• This produced timestamps far in the future (~year 65,000), causing 400 Bad Request from the Datadog API
• Fixed by using time.UnixMilli() instead of time.Unix()

Test plan

• Run pup logs search --query="status:error" --from="1h" and verify it returns results instead of 400
• Run pup logs search --query="*" --from="30m" --limit=5 to confirm basic queries work

🤖 Generated with Claude Code

[github-actions]

📊 Test Coverage Report

Overall Coverage: 75.5%

Threshold: 80% ❌

Coverage by Package

## Coverage by Package

- github.com/DataDog/pup/pkg/auth/callback/server.go:40: 81.2%
- github.com/DataDog/pup/pkg/auth/dcr/client.go:28: 100.0%
- github.com/DataDog/pup/pkg/auth/dcr/types.go:24: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/client.go:22: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/pkce.go:24: 85.7%
- github.com/DataDog/pup/pkg/auth/storage/factory.go:53: 94.7%
- github.com/DataDog/pup/pkg/auth/storage/keychain.go:44: 42.9%
- github.com/DataDog/pup/pkg/auth/storage/storage.go:58: 71.4%
- github.com/DataDog/pup/pkg/auth/types/types.go:23: 100.0%
- github.com/DataDog/pup/pkg/client/client.go:33: 94.4%
- github.com/DataDog/pup/pkg/config/config.go:22: 100.0%
- github.com/DataDog/pup/pkg/formatter/formatter.go:31: 100.0%
- github.com/DataDog/pup/pkg/util/time.go:20: 95.8%

## Summary

total:								(statements)		75.5%

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📈 Coverage Status: ❌ FAILED - Coverage below minimum threshold

_{Updated for commit 0dda97c}