perf: Remove unnecessary allocation and construction of a HashMap in Signature::parse

[mennovf]

Summary

I noticed Signature::parse constructs a temporary HashMap for some reason. I removed this allocation and weird construction to speed up the parsing. I see no need for the wasteful temporary.

Checklist

• ran cargo make fmt
• using conventional commits to hightlight user-facing fixes and features

[mzeitlin11]

Thanks for the pr, this looks good to me! Is pretty similar to the implementation in the next branch, but good to get in sooner.

Only semantic difference looks like missing = in signature chunk is ignored here, vs errored in next branch implementation.

[mennovf]

I was unaware of the ongoing effort on the next branch when I made this pull request. I could copy over its code into this pull request or just close it and wait for next.

[arlyon]

I am ok with backporting it, running CI

[arlyon]

Hello, @mennovf, I have recently merged some changes to bump msrv and fix the CI issues. Please rebase when you have the chance :)