Depreciated functions used in ChartColorTemplates

* [ X ] I've read, understood, and done my best to follow the [*CONTRIBUTING guidelines](https://github.com/jjatie/Charts/blob/master/CONTRIBUTING.md).

## What did you do?

Updated iOS Deployment Target for Pods to 15.0

## What did you expect to happen?

No warnings

## What happened instead?

Warnings indicating depreciated functions used in ChartColorTemplates:
- scanString(_:into:)
- scanCharacters(from:into:)
- scanInt32
- scanFloat

## DGCharts Environment

**DGCharts version/Branch/Commit Number: 5.1.0 **
**Xcode version: Version 15.1 (15C65)**
**Swift version: 5.7.2**
**Platform(s) running DGCharts: iMac**
**macOS version running Xcode: 14.1.2 (23B92)**

Start in ChartColorTemplates and inspect its uses of scanString(_:into:), scanCharacters(from:into:), scanInt32, and scanFloat. Build DGCharts with the reported Xcode environment to reproduce the warnings, then verify the updated implementation builds without those deprecation warnings.

Written by the indexing model from the issue text.