release: bump 0.8.6 -> 0.8.7 (#263)

Version bump `0.8.6` → `0.8.7`.

### Added
- R binding: a *Getting started* vignette and a synthetic `sample_ohlcv` example dataset, giving new users a runnable, self-contained walkthrough and populating the R-universe Articles and Datasets tabs. The vignette's code is exercised in CI so a broken example is caught before the published build. (#262)

Bump touches the manual release touchpoints only; docs/webpage version strings are left to `sync-about.yml` on the tag.

Cargo.toml

@@ -14,7 +14,7 @@ members = [
 exclude = ["fuzz"]
 
 [workspace.package]
-version = "0.8.6"
+version = "0.8.7"
 authors = ["kingchenc <support@wickra.org>"]
 edition = "2021"
 rust-version = "1.86"
@@ -26,7 +26,7 @@ keywords = ["finance", "trading", "indicators", "technical-analysis", "ta"]
 categories = ["finance", "mathematics", "science"]
 
 [workspace.dependencies]
-wickra-core = { path = "crates/wickra-core", version = "0.8.6" }
+wickra-core = { path = "crates/wickra-core", version = "0.8.7" }
 
 thiserror = "2"
 rayon = "1.10"