Refactor batcher and inline into SessionKeeper

This commit does these things:
- Inlines batching flag to SessionKeeper, removing batcher entirely
as a separate entity with all of its logic(threshold, traffic trigger).
- Emits all actions from SessionKeeper if batching is enabled when
an action is added. This works nicely if we can guarantee that actions
are gonna be a multiple of some T which is the case as currently we
target T=70s for proxy, direct, vpn, stun keepalives. This also makes
thresholds and the whole logic around them irrelevant.

Traffic triggered batching implementation was doing more harm than good
since it triggers on _any_ traffic, meaning even when alignment was
achieved, it might misalign since any traffic triggers it.

Feature flags are not removed in this commit so not to push for
version update of libtelio, so now they are no-op.

Signed-off-by: Lukas Pukenis <[email protected]>

Signed-off-by: Lukas Pukenis <[email protected]>

.unreleased/LLT-5857

@@ -0,0 +1 @@
+Refactor batcher