feat: add new schema builder methods which allow GC to collect built schemas

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 21.42857% with 11 lines in your changes missing coverage. Please review.

Project coverage is 99.58%. Comparing base (8e9d97c) to head (056b7e3). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
datamodel/high/base/schema_proxy.go	0.00%	11 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #334 +/- ## ========================================== - Coverage 99.65% 99.58% -0.07% ========================================== Files 164 164 Lines 16674 16687 +13 ========================================== + Hits 16616 16618 +2 - Misses 53 64 +11 Partials 5 5 ``` | [Flag](https://app.codecov.io/gh/pb33f/libopenapi/pull/334/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pb33f) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/pb33f/libopenapi/pull/334/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pb33f) | `99.58% <21.42%> (-0.07%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pb33f#carryforward-flags-in-the-pull-request-comment) to find out more.

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