Support federated query mysql bit_length function

# Background

Hi Community,

Federated queries help users perform cross-database join queries, subqueries, and aggregate queries. Currently, we plan to enhance MySQL functions in the federated query environment to support more SQL execution scenarios in federated query contexts.

For more details, please refer to: [Apache ShardingSphere Documentation on SQL Federation](https://shardingsphere.apache.org/document/current/cn/features/sql-federation/).

Ref: https://dev.mysql.com/doc/refman/8.4/en/string-functions.html#function_bit-length

# Task

- [ ] `select bit_length('\n\t\r\b\0\_\%\\');`

Run log:
```
expected:
+----------------------------------+
| bit_length('\n\t\r\b\0\_\%\\') |
+==================================+
| 80 |
+----------------------------------+

actual:
SQL federation does not support SQL 'select bit_length('\\n\\t\\r\\b\\0\\_\\%\\\\');\n'.\nMore details: At line 0, column 0: No match found for function signature bit_length()
```

- [ ] TODO Test cases for nested function calls

Use the provided SELECT bit_length('\n\t\r\b\0\_\%\\') as the reproduction case and start by tracing MySQL function support in SQL federation. Add support for the bit_length query, then add the requested nested-function test cases and verify the result is 80 rather than an unsupported-function error.

Written by the indexing model from the issue text.