[I] [rust] get_table returns InvalidTableException for a nonexistent table [fluss]

["adamrecsko (via GitHub)" <gi...@apache.org>]

adamrecsko opened a new issue, #4270:
URL: https://github.com/apache/fluss/issues/4270

   ### Search before asking
   
   - [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.
   
   
   ### Fluss version
   
   main (development)
   
   ### Please describe the bug 🐞
   
      When the Rust client calls `FlussConnection::get_table` for a table that does not exist, it returns the generic `InvalidTableException` instead of `TableNotExist`.
   
     This prevents applications from reliably distinguishing a missing table from other metadata or network-related failures.
   
     ### Expected behavior
   
     - A nonexistent table returns `FlussError::TableNotExist`.
     - Network, timeout, and other RPC errors retain their original error type.
   
     ### Steps to reproduce
   
     ```rust
     let table_path = TablePath::new("fluss", "nonexistent_table");
     let result = connection.get_table(&table_path).await;
   
     let error = match result {
         Ok(_) => panic!("getting a nonexistent table should fail"),
         Err(error) => error,
     };
   
     assert_eq!(
         error.api_error(),
         Some(FlussError::TableNotExist)
     );
   ```
     ### Actual result
   
     FlussError::InvalidTableException
   
     ### Expected result
   
     FlussError::TableNotExist
   
   ### Solution
   
    Before refreshing the table metadata, use the authoritative GetTable RPC to check whether the table exists.
   
    If `GetTable` indicates that the table does not exist, return a typed `Error::table_not_exist` error. Propagate all other RPC and network errors unchanged.
   
     Conceptually:
     ```rust
     if metadata.fetch_table_id(table_path).await?.is_none() {
         return Err(Error::table_not_exist(format!(
             "Table not found: {table_path}"
         )));
     }
     
     metadata.update_table_metadata(table_path).await?;
   ```
   This preserves the distinction between a missing table and transient network or server failures.
   
   Add an integration test verifying that `FlussConnection::get_table` returns `FlussError::TableNotExist` for a nonexistent table.
   
   ### Are you willing to submit a PR?
   
   - [x] I'm willing to submit a PR!


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