chore(release): roll up v0.3.0 — expensive-eval, gradient-free, multi-fidelity

CHANGELOG entry for the v0.3.0 cohort, version bump in Cargo.toml and
README. Theme: filling heuropt's expensive-evaluation and constraint-
handling gaps.

Algorithms (9 new): OnePlusOneEs, NelderMead, IpopCmaEs, BayesianOpt,
SeparableNes, Tpe, Hyperband.

Operators (1 new): LevyMutation. Repair operators (1 trait + 2 impls):
Repair<D> with ClampToBounds and ProjectToSimplex.

Selection helpers (1 new): stochastic_ranking_select.

Internal helpers: Cholesky factorization (used by BO).

API additions:
- CmaEsConfig.initial_mean: Option<Vec<f64>> (None preserves existing
  midpoint-of-bounds behavior; used by IpopCmaEs to inject restart
  diversity).
- New PartialProblem trait — multi-fidelity contract used by
  Hyperband.

No breaking changes to v0.2.0 public API.

README.md

@@ -17,13 +17,13 @@ framework concepts.
 
 ```toml
 [dependencies]
-heuropt = "0.2"
+heuropt = "0.3"
 
 # Optional features:
 # - "serde":     derive Serialize/Deserialize on the core data types.
 # - "parallel":  evaluate populations across rayon's thread pool.
 #                Seeded runs stay bit-identical to serial mode.
-# heuropt = { version = "0.2", features = ["serde", "parallel"] }
+# heuropt = { version = "0.3", features = ["serde", "parallel"] }
 ```
 
 ## Define a problem