fix: increase NFS timeout from 1s to 5s to allow valid mounts to succeed

**Problem:**
NFS mounts were failing with "Mount failed after 3 attempts" even for valid,
working shares like nfs://192.168.1.224/var/nfs/shared/data.

**Root Cause:**
The timeo=10 (1 second RPC timeout) option added in commit 5ade992 was too
aggressive. Valid NFS mounts on local networks can take >1 second due to:
- Server load and disk I/O
- NFS protocol handshake overhead
- Network conditions

**Solution:**
Increased timeo from 10 (1s) to 50 (5s):
- Allows valid mounts to succeed even with server load
- Still provides reasonably fast failure (~20-25s total for non-existent shares)
- Maintains fail-fast behavior with soft mount option

**Impact:**
- Valid shares: Now succeed within 5 seconds
- Invalid shares: Fail in ~20-25 seconds (vs previous 150+ seconds before commit 5ade992)
- Balanced approach between fast failure and mount success

Files modified:
- src/mount/drivers/nfs.rs: Changed timeo=10 to timeo=50
- tests/unit/mount_drivers_test.rs: Updated test assertion

Author: doomedramen

src/mount/drivers/nfs.rs

@@ -310,7 +310,7 @@ impl MountHandler for NfsHandler {
     fn get_default_options(&self) -> Vec<String> {
         vec![
             "nolock".to_string(),    // No remote locking (avoids rpc.statd requirement)
-            "timeo=10".to_string(),  // RPC timeout: 1 second (10 * 0.1s)
+            "timeo=50".to_string(),  // RPC timeout: 5 seconds (50 * 0.1s)
             "retrans=2".to_string(), // Retransmission attempts before failing
             "soft".to_string(),      // Fail fast instead of hanging indefinitely
             "_netdev".to_string(),   // Proper network device handling

tests/unit/mount_drivers_test.rs

@@ -703,8 +703,8 @@ fn test_nfs_default_options_include_timeouts() {
 
     // Verify NFS timeout options are present for fast failure
     assert!(
-        options.contains(&"timeo=10".to_string()),
-        "Should include timeo=10 for 1-second RPC timeout"
+        options.contains(&"timeo=50".to_string()),
+        "Should include timeo=50 for 5-second RPC timeout"
     );
     assert!(
         options.contains(&"retrans=2".to_string()),