feat: add Sobol quasi-random sampler behind sobol feature flag

Add SobolSampler using Owen-scrambled Sobol sequences (sobol_burley
crate) for better uniform coverage of the parameter space compared to
random sampling. Supports all distribution types including log-scale
and stepped parameters.

Cargo.toml

@@ -24,6 +24,7 @@ optimizer-derive = { version = "0.1.0", path = "optimizer-derive", optional = tr
 serde = { version = "1", features = ["derive"], optional = true }
 serde_json = { version = "1", optional = true }
 tracing = { version = "0.1", optional = true }
+sobol_burley = { version = "0.5", optional = true }
 
 [features]
 default = []
@@ -31,6 +32,7 @@ async = ["dep:tokio"]
 derive = ["dep:optimizer-derive"]
 serde = ["dep:serde", "dep:serde_json"]
 tracing = ["dep:tracing"]
+sobol = ["dep:sobol_burley"]
 
 [dev-dependencies]
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "time"] }