chore(release): bump to v0.2.0 and update CHANGELOG

Substantial v0.2.0 release on top of v0.1.0:

**21 new algorithms:**
- Single-objective: HillClimber, SimulatedAnnealing, GeneticAlgorithm,
  ParticleSwarm, CmaEs, TabuSearch, AntColonyTsp, Umda, Tlbo
- Multi-objective: Mopso, Ibea, SmsEmoa, Hype, Rvea, PesaII,
  EpsilonMoea, AgeMoea, Grea, Knea

**5 new operators:**
BoundedGaussianMutation, SimulatedBinaryCrossover (SBX),
PolynomialMutation, CompositeVariation, LevyMutation

**New utility:** `hypervolume_nd` (HSO algorithm) for arbitrary
dimensionality

**New examples:** `compare` (multi-seed harness across 7 benchmark
problems and 19 algorithms), `benchmarks` (canonical reference runs),
`jiggly_tuning` (real-world 4-objective firmware tuning)

**New feature flag:** `parallel` (rayon-backed population evaluation)

**README:** added an explanatory algorithm-selection decision tree

No breaking changes to v0.1.0 public API.

README.md

@@ -17,13 +17,13 @@ framework concepts.
 
 ```toml
 [dependencies]
-heuropt = "0.1"
+heuropt = "0.2"
 
 # 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 = "0.1", features = ["serde", "parallel"] }
+# heuropt = { version = "0.2", features = ["serde", "parallel"] }
 ```
 
 ## Define a problem