Polish for Release

[steve-downey]

Fix file names in code
Add all licenses
Check SPDX ids
Document installtest
Update python pinned deps in requirements-dev
Update README
Add devcontainer/.devcontainer.json for github codespaces
Permission checks in github actions

[github-advanced-security]

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[coveralls]

Pull Request Test Coverage Report for Build 20440769640

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 99.038%

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Files with Coverage Reduction	New Missed Lines	%
include/beman/optional/optional.hpp	2	98.99%

Totals
Change from base Build 20432735531:	-0.1%
Covered Lines:	309
Relevant Lines:	312

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💛 - Coveralls