fix: replace all unstable is_multiple_of with modulo operator

Rust's is_multiple_of is an unstable feature (issue #128101).
Replace with standard modulo operator for compatibility with stable Rust.

apps/synord/src/main.rs

@@ -494,7 +494,7 @@ async fn import_blocks(
             errors += 1;
         } else {
             imported += 1;
-            if imported.is_multiple_of(1000) {
+            if imported % 1000 == 0 {
                 info!("Imported {} blocks...", imported);
             }
         }
@@ -586,7 +586,7 @@ async fn export_blocks(
                 writer.write_all(&serialized)?;
 
                 exported += 1;
-                if exported.is_multiple_of(1000) {
+                if exported % 1000 == 0 {
                     info!("Exported {} blocks...", exported);
                 }
             }

crates/synor-mining/src/kheavyhash.rs

@@ -166,7 +166,7 @@ impl KHeavyHash {
             }
 
             // Report progress every 10000 hashes
-            if tried.is_multiple_of(10000) && !callback(tried, nonce) {
+            if tried % 10000 == 0 && !callback(tried, nonce) {
                 return None; // Cancelled
             }
         }

crates/synor-mining/src/miner.rs

@@ -282,7 +282,7 @@ impl BlockMiner {
             nonce = nonce.wrapping_add(1);
 
             // Update stats periodically
-            if hashes.is_multiple_of(10000) {
+            if hashes % 10000 == 0 {
                 self.hash_counter.fetch_add(10000, Ordering::Relaxed);
             }
         }

crates/synor-storage/src/chunker.rs

@@ -139,7 +139,7 @@ impl Chunker {
     pub fn chunk_count(&self, file_size: u64) -> u32 {
         let size = file_size as usize;
         let full_chunks = size / self.config.chunk_size;
-        let has_remainder = !size.is_multiple_of(self.config.chunk_size);
+        let has_remainder = size % self.config.chunk_size != 0;
         
         (full_chunks + if has_remainder { 1 } else { 0 }) as u32
     }

crates/synor-storage/src/proof.rs

@@ -187,7 +187,7 @@ impl MerkleTree {
         let mut level_size = self.leaf_count;
 
         while level_size > 1 {
-            let sibling_idx = if idx.is_multiple_of(2) {
+            let sibling_idx = if idx % 2 == 0 {
                 idx + 1
             } else {
                 idx - 1