Support Parsers.jl 3 for interoperability with CSV.jl 1.0

## Summary

FixedPointDecimals v0.6.5 requires `Parsers = "2.7.0 - 2"`, while CSV.jl v1.0.0 requires `Parsers = "3"`. Because an environment can contain only one version of Parsers, the current versions cannot be installed together.

This matters in environments using DuckDB.jl, which depends on FixedPointDecimals. A normal update may retain CSV 0.10.x rather than move to CSV 1.0 if it would need to replace the current dependency set.

## Reproducer

With a General registry containing CSV 1.0.0, these exact versions have incompatible Parsers requirements:

```julia
using Pkg
Pkg.activate(; temp=true)
Pkg.add([
PackageSpec(name="FixedPointDecimals", version=v"0.6.5"),
PackageSpec(name="CSV", version=v"1.0.0"),
])
```

The relevant registered compat entries are:

- FixedPointDecimals 0.6.5: `Parsers = "2.7.0 - 2"`
- CSV 1.0.0: `Parsers = "3"`

## References

- FixedPointDecimals compat: https://github.com/JuliaRegistries/General/blob/master/F/FixedPointDecimals/Compat.toml
- CSV compat: https://github.com/JuliaRegistries/General/blob/master/C/CSV/Compat.toml
- FixedPointDecimals parser implementation: https://github.com/JuliaMath/FixedPointDecimals.jl/blob/master/src/parse.jl

Start by running the exact Julia Pkg reproducer, then inspect the parser implementation referenced in src/parse.jl and the package compatibility entries. Update the Parsers support so FixedPointDecimals can be installed with CSV.jl 1.0, and verify that the reproducer resolves successfully without breaking existing parsing behavior.

Written by the indexing model from the issue text.