Refactor copy lambda

[devhl-labs]

The copy lambda had a hard coded command that mutated the cached value. That was giving me an issue in another PR I'm working on. I removed that, and I also moved the white space handling from paste to copy. The reason for that change is that the way we handle white space will depend on how the copy is written. For example, these two will produce different results. Therefore, we should handle the white space correctly in the copy lambda where it occurs, not later in the paste.

{{#lambda.copy}}foo{{/lambda.copy}}

{{#lambda.copy}}
foo
{{/lambda.copy}}

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[wing328]

thanks for the PR

what about adding some tests similar to those in https://github.com/OpenAPITools/openapi-generator/tree/master/modules/openapi-generator/src/test/java/org/openapitools/codegen/templating/mustache ?

[devhl-labs]

done