db.mysql: Add local_infile option to Config for LOAD DATA LOCAL INFILE support. #71

Describe the feature

Summary The db.mysql module currently does not support LOAD DATA LOCAL INFILE, which is the fastest way to bulk-load data into MySQL (typically 10-20x faster than multi-value INSERT statements). This is because MYSQL_OPT_LOCAL_INFILE must be set via mysql_options() before mysql_real_connect(), but DB.conn is a private field, making it impossible for users to call C.mysql_options() from outside the module.

Current Problem When bulk-loading a 570K-row, 61-column CSV file:

Multi-value INSERT (current approach): ~33 seconds LOAD DATA LOCAL INFILE (if available): estimated ~2-3 seconds The performance gap is significant for any data ingestion use case.

Proposed Solution Add a local_infile field to mysql.Config:

 
pub struct Config {
pub:
    host       string
    port       u32    = 3306
    user       string
    password   string
    dbname     string
    local_infile bool = false  // <-- new field
}```
In the connect() function, before calling C.mysql_real_connect():


```c
 
if config.local_infile {
    C.mysql_options(conn, C.MYSQL_OPT_LOCAL_INFILE, &true_val)
}```
This is a minimal, backward-compatible change — local_infile defaults to false, so existing code is unaffected.

### Use Case

Use Case Example

```v
 
import db.mysql

mut db := mysql.connect(
    host:        '127.0.0.1'
    port:        3306
    user:        'root'
    password:    ''
    dbname:      'mydb'
    local_infile: true   // <-- enable LOAD DATA LOCAL INFILE
)!```

// Now LOAD DATA LOCAL INFILE works
db.exec_none("LOAD DATA LOCAL INFILE '/path/to/data.csv' INTO TABLE mytable FIELDS TERMINATED BY ',' ENCLOSED BY '\"' LINES TERMINATED BY '\\n' IGNORE 1 LINES")
Alternative Considered
Using StmtHandle.execute() with prepared statements for batch inserts, but StmtHandle reallocates bind arrays on every call (see stmt.c.v:844), making it slower than multi-value INSERT for large batches.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### Version used

V lastest

### Environment details (OS name and version, etc.)

V version: latest
MySQL: 8.0+
OS: Linux (WSL)
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