Resolve Decimal version to use v3

[jaeyson]

https://github.com/jaeyson/ex_typesense/actions/runs/27087439421/job/79944558195

Run mix deps.audit
Name: decimal
Version: 2.4.1
Lockfile: /home/runner/work/ex_typesense/ex_typesense/mix.lock
URL: https://github.com/advisories/GHSA-rhv4-8758-jx7v
Title: Decimal: Unbounded exponent in `Decimal.new` enables unauthenticated DoS
Severity: moderate
Vulnerable versions: >= 0.1.0, < 3.0.0
First patched versions: 3.0.0

Vulnerabilities found!