chore(antithesis): Alter dogstatsd generation to is_malformed regime (#2215)

## Summary
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Our previous approach to generating dogstatsd load for use in the
Antithesis rig was very Datadog/lading inspired: generate something
that is correct-by-construction and then bias the result to be
'interesting'. This works well but the biasing systematically avoids
conditions that are not-malformed -- that is, accepted by the SUT --
but are demonstrative of goofy behavior. This commit changes the
generator to be a hybrid of that approach with a state search approach.
We define a predicate `is_malformed` that confirms whether or not
a payload will be accepted by the SUT and then payloads which are not
malformed, however strange, are transmitted.

## Change Type
- [ ] Bug fix
- [ ] New feature
- [x] Non-functional (chore, refactoring, docs)
- [ ] Performance


## How did you test this PR?
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## References

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Author: blt

Cargo.lock

@@ -24,6 +24,7 @@ ryu = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 serde_yaml = { workspace = true }
+simdutf8 = { workspace = true }
 
 [dev-dependencies]
 proptest = { workspace = true }

test/antithesis/harness/Cargo.toml

@@ -5,3 +5,4 @@
 # It is recommended to check this file in to source control so that
 # everyone who runs the test benefits from these saved cases.
 cc 377cba92b14295b3fe5c6f2738a398ee042be8e35f529398ecf9e275e6b0a1da # shrinks to seed = 0
+cc 1f807f27fdbf0b983fc773b815b21d6023e1bce87691d07133b438b862edcc5b # shrinks to seed = 6079028945602138863, limit_bytes = 21