feat: make `parse_float_as_decimal` work on scientific notaion

### Is your feature request related to a problem or challenge?

Datafusion can't parse float as decimal if it is scientific notation.

``` bash
DataFusion CLI v33.0.0
❯ set datafusion.sql_parser.parse_float_as_decimal=true;
0 rows in set. Query took 0.014 seconds.

❯ select 10e10;
SQL error: ParserError("Cannot parse 10e10 as i128 when building decimal: invalid digit found in string")
❯ select -10e10;
SQL error: ParserError("Cannot parse 10e10 as i128 when building decimal: invalid digit found in string")
```

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by tracing the parse_float_as_decimal setting through DataFusion's SQL parser and reproduce the reported SELECT 10e10 and SELECT -10e10 queries. Identify the existing decimal-literal tests, then add coverage for scientific notation and confirm the queries parse successfully when the setting is enabled.

Written by the indexing model from the issue text.