Sol v0.8

[RyanRHall]

This PR does the following:

• upgrades the strings library to sol v0.8
• updates the ds-test submodule to latest version (needed for the unlocked pragma)
• adds a CI workflow (to hopefully make future changes easier)

[zbcoding]

Nice
A few new additions building on https://github.com/Arachnid/solidity-stringutils/pull/45/files

[tempe-techie]

Nice work!

@Arachnid Can you please merge this pull request? This brings the library from the 0.4 to the 0.8 Solidity version, which is absolutely necessary.

[tempe-techie]

@RyanRHall I'm getting this warning in the hardhat console:

Warning: This declaration shadows an existing declaration.

45 |     function memcpy(uint dest, uint src, uint len) private pure {

This is because the len attribute has the same name as the function len().

The code still works, nothing serious, but it would make sense to rename the len attribute in memcpy to _len or something else.

[tempe-techie]

Also adding SPDX-License-Identifier would be beneficial, but this is something @Arachnid needs to decide since he wrote the library.

EDIT: Nevermind, I see the repo already has a license (Apache v2), so this identifier should be added on top of the Solidity file: // SPDX-License-Identifier: Apache-2.0

[hellwolf]

wen merge?

[hellwolf]

thank you @Arachnid !