pkg/query/flamegraph_arrow: Properly calculate height

[metalmatze]

Previously the height was estimated, but didn't take inlined functions and injected label nodes into account.

[metalmatze]

I've also updated Go to 1.21 to use the new max keyword. 🙂

[alwaysmeticulous]

✅ Meticulous spotted zero visual differences across 211 screens tested: view results.

_{Last updated for commit 8d114c8. This comment will update as new commits are pushed.}