feat: implement basic f4 support

[Stebalien]

• Auto-create embryos on send.
• Allow overwriting embryo actors (used by the init actor).

[codecov-commenter]

Codecov Report

Merging #897 (5079dc9) into master (08c29e6) will decrease coverage by 2.34%. The diff coverage is 19.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #897      +/-   ##
==========================================
- Coverage   51.57%   49.23%   -2.35%     
==========================================
  Files         124      124              
  Lines       10406    10936     +530     
==========================================
+ Hits         5367     5384      +17     
- Misses       5039     5552     +513     

Impacted Files	Coverage Δ
fvm/src/account_actor.rs	0.00% <ø> (ø)
fvm/src/call_manager/default.rs	0.00% <0.00%> (ø)
fvm/src/kernel/default.rs	13.34% <0.00%> (-1.66%)	:arrow_down:
fvm/src/syscalls/actor.rs	0.00% <0.00%> (ø)
fvm/src/syscalls/mod.rs	0.00% <0.00%> (ø)
sdk/src/actor.rs	0.00% <0.00%> (ø)
fvm/src/machine/manifest.rs	36.15% <33.33%> (-12.17%)	:arrow_down:
fvm/src/state_tree.rs	66.27% <71.42%> (-14.69%)	:arrow_down:
shared/src/address/mod.rs	66.46% <100.00%> (-22.52%)	:arrow_down:
... and 7 more

[Stebalien]

TODO:

• Drop conformance tests?
• Test embryo creation.

[Stebalien]

• [ ] TODO: An integration test that:
  1. Exec4s a new actor, new actor checks it's f4 address with lookup_address.
  2. Sends to create an embryo, Exec4s over that embryo, also looks up the address with lookup_address.
• [ ] TODO: An integration test that calls lookup_address when no f4 address is assigned.
• [ ] TODO: An integration test that calls lookup_address on an account.

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edit: later. I've added some basic lookup_address and embryo tests, but the tests I wanted to write here have a chicken/egg problem with merging these changes into the actors.