This applies to all span data entities that are slices: Annotations,
Links, and Message Events.

At the limit, it pops the oldest sample off prior to appending the new
sample. This should not cause an additional allocation.

Each entity shares the same WithBufferLimit option following the YAGNI
principle.

Each test ensures 4 entities are added in total -- the first 2 are
dropped and the last 2 remain. This should prevent off by 1 bugs.

This applies limits to span data entities that are slices: Attributes,
Message Events, and Links.

The limits are default per the spec and can be globally changed with
trace.ApplyConfig.

The limits can also be changed per-span when creating a new span
with one or more trace.StartOption.

At the limit, it pops the oldest sample off prior to appending the new
sample.

Each test ensures 4 entities are added in total -- the first 2 are
dropped and the last 2 remain. This should prevent off by 1 bugs.