feat: add rows inserted, deleted and completed metrics

[murex971]

Summary

• Count rows affected by INSERT / UPDATE / DELETE from Postgres CommandComplete tags

Test

• Unit tests for CommandComplete tag/rows parsing
• Unit tests for Count Add/Sub/Div including new fields

[codecov]

Codecov Report

❌ Patch coverage is 98.20359% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog-stats/src/server.rs	50.00%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!

[levkk]

Looks great, just one small function signature change and we should be good to merge.

[murex971]

@levkk ready 😛

[levkk]

Amazing, thank you!