feat: add castMapping function

[aleclarson]

Tip

The owner of this PR can publish a preview release by commenting /publish in this PR. Afterwards, anyone can try it out by running pnpm add radashi@pr<PR_NUMBER>.

Summary

This will be used by #36 to provide similar functionality in the min and max Radashi functions.

The castMapping function is primarily intended for use by other utility functions that would like to support a multitude of possible (and potentially optional) mapping strategies.

// The created “mapping function” always takes a single argument.
const getFooProperty = castMapping('foo')
const getHalved = castMapping((arg: number) => arg / 2)

getFooProperty({ foo: 1 }) // => 1
getHalved(200) // => 100

What kind of change does this PR introduce?

Feature

For any code change,

• Related documentation has been updated, if needed
• Related tests have been added or updated, if needed

Does this PR introduce a breaking change?

No

Bundle impact

Status	File	Size
A	src/casted/castMapping.ts	116