[performance] update go-structr and go-mutexes with memory usage improvements

[NyaaaWhatsUpDoc]

Description

Updates:

• go-mutexes -> v1.5.0, mutex map now performs self-compaction if reduced in size by loadFactor / 2, also uses swiss hashmap implementation
• go-structr -> v0.8.4 uses swiss hashmap implementation, compacts specifically queue indices if reduced in size by loadFactor / 2, fix for loading cache entry items in LoadOne(), other unrelated (for us) fix

Checklist

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have not leveraged AI to create the proposed changes.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.