reduce duplication in single source file

[goatshriek]

Keep track of top-level headers that have already been included for source files in the single file source. This results in faster file generation and a smaller single file.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.54%. Comparing base (f8368cd) to head (0177f2e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## latest #409 +/- ## ======================================= Coverage 90.54% 90.54% ======================================= Files 46 46 Lines 4188 4188 Branches 556 556 ======================================= Hits 3792 3792 Misses 273 273 Partials 123 123 ```

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud