Performance: fix memory leak

[olafurpg]

Fixes CODY-3616
Previously, the Cody extension in all IDEs (including VS Code and JetBrains) had a memory leak causing the process to consume multiple GB of memory after long usage. This PR fixes this issue by calling tree.delete() on tree-sitter ASTs after they are evicted from an LRU cache.

The fix itself is a one-liner. Most of the diff in this PR is adding the reproduction in memory.test.ts, which is a test that we skip by default but I think it's helpful to keep ti in the repo as documentation on how to reproduce memory leaks in the future.

Test plan

• Follow instructions in memory.test.ts to download and convert Cody NES recordings.
• Run the "replay" test with and without the second commit of this PR where we delete trees on LRU eviction.

# Before, reach 2gb "external" heap after processing only 200 editor events
stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 0, heapUsed: '-170952.00 B', external: '-1013.00 B' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 50, heapUsed: '36.85 MB', external: '115.02 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 100, heapUsed: '38.91 MB', external: '590.83 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 150, heapUsed: '35.38 MB', external: '1.14 GB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 200, heapUsed: '42.41 MB', external: '1.70 GB' }

stdout | src/memory.test.ts > Memory Usage > replay
<empty line>
stderr | src/memory.test.ts > Memory Usage > replay
----stderr----
Aborted()
--------------
----stderr----
Aborted()

# After, the "external" heap is stable at ~32mb
stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 0, heapUsed: '-71456.00 B', external: '-1413.00 B' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 50, heapUsed: '41.70 MB', external: '32.30 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 100, heapUsed: '43.79 MB', external: '32.49 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 150, heapUsed: '40.27 MB', external: '32.04 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 200, heapUsed: '47.41 MB', external: '32.27 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 250, heapUsed: '48.65 MB', external: '32.47 MB' }

stdout | src/memory.test.ts > Memory Usage > replay
{ totalEvents: 300, heapUsed: '49.43 MB', external: '32.16 MB' }
...

Changelog

• Fixed a memory leak where Cody would sometimes use several GB of memory after long use.

[abeatrix]

I dont really know how it works to give concrete feedback but the test results lgtm. Approve to unblock!

[olafurpg]

@abeatrix the short explanation of this fix is that tree-sitter trees are not garbage collected by default, they are stored on the Node.js "external" heap and we have to explicitly free them with .delete(). FYI @valerybugakov

[valerybugakov]

🚀