Introduce lading_antithesis

I am gearing up to add Antithesis rig to this project, my rough goal
being to eventually absorb and then expand on the existing integration
test mechanism. There will be a couple of 'ducks' and 'sheepdog' in the
project up-stack from this, I imagine.

This new crate wraps the Antithesis Rust SDK and gives SUT assertions a
more tidy appearance. This is ported from my work on Datadog/saluki.

Author: blt

Cargo.lock

@@ -4,6 +4,7 @@ members = [
   "integration/sheepdog",
   "integration/ducks",
   "lading",
+  "lading_antithesis",
   "lading_capture_schema",
   "lading_capture",
   "lading_fuzz",
@@ -69,6 +70,7 @@ ddsketch-agent = { git = "https://github.com/DataDog/saluki", rev = "f47a7ef588c
 datadog-protos = { git = "https://github.com/DataDog/saluki", rev = "f47a7ef588c53aa1da35dcfd93808595ebeb1291" }
 protobuf = { version = "3.7" }
 enum_dispatch = { version = "0.3" }
+antithesis_sdk = { git = "https://github.com/antithesishq/antithesis-sdk-rust", rev = "78c9db56771f0f6b01cb5404765c5a96852c159c", default-features = false } # 0.2.8 is pinned to rand 0.8, rev version allows us to select workspace rand
 
 [workspace.lints.clippy]
 all = "deny"

Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "lading-antithesis"
+version = "0.1.0"
+authors = [
+  "Brian L. Troutwine <brian.troutwine@datadoghq.com>",
+  "George Hahn <george.hahn@datadoghq.com",
+]
+edition = "2024"
+license = "MIT"
+repository = "https://github.com/datadog/lading/"
+keywords = ["random_test", "generator"]
+categories = ["development-tools::profiling"]
+description = "A tool for load testing daemons."
+
+[features]
+antithesis = ["dep:antithesis_sdk", "antithesis_sdk/full", "dep:serde_json"]
+
+[dependencies]
+antithesis_sdk = { workspace = true, optional = true }
+serde_json = { workspace = true, optional = true }
+
+[lib]
+doctest = false
+
+[lints]
+workspace = true

lading_antithesis/Cargo.toml

@@ -0,0 +1,15 @@
+# lading-antithesis
+
+A thin facade over the [Antithesis](https://antithesis.com) Rust SDK for the
+lading project. It owns the single `antithesis` cargo feature: with the feature
+off (the default) every macro is a no-op that elides its arguments unevaluated,
+so ordinary lading builds are unaffected; with it on, each macro forwards to the
+underlying SDK macro.
+
+Both lading's SUT bootstrap (`lading/src/antithesis_hooks.rs`) and the Antithesis
+workload drivers under `antithesis/` reach the SDK through this crate, never
+`antithesis_sdk` directly, so an assertion reads identically wherever it lives.
+
+Prefer the numeric macros (`always_gt!`, `always_le!`, ...) over
+`always!(x > y, ...)`: a more precise assertion gives Antithesis better
+exploration.