Investigate Non-determinstic memory allocations

[jmayclin]

Problem:

In the CI runs for #5592 we were seeing non-determinstic max memory usage

static memory: 959380
config: 19281
connection_init: 61498
handshake in progress: 112529
handshake complete: 86423
application data: 86423
max usage: 150424
actual: 19281, expected: 19259
actual: 61498, expected: 61482
actual: 112529, expected: 112505
actual: 86423, expected: 86399
actual: 86423, expected: 86399
actual: 150424, expected: 163114

https://github.com/aws/s2n-tls/actions/runs/18926451616/job/54034406327

 static memory: 959380
config: 19281
connection_init: 61498
handshake in progress: 112529
handshake complete: 86423
application data: 86423
max usage: 163114
actual: 19281, expected: 19259
actual: 61498, expected: 61482
actual: 112529, expected: 112505
actual: 86423, expected: 86399
actual: 86423, expected: 86399
actual: 163114, expected: 150378

https://github.com/aws/s2n-tls/actions/runs/18926149221/job/54033491972

150424 vs 163114

Solution:

1. where is this variance coming from? If we only measure s2n-tls memory usage (and not aws-lc usage) do we still see this variance?
2. can probably look at the dhat report for further deep dives

Also, I can't reproduce this locally 🥲