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.lock

@@ -1944,7 +1944,7 @@ dependencies = [
 
 [[package]]
 name = "wickra"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "approx",
  "criterion",
@@ -1955,7 +1955,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-bench"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "criterion",
  "kand",
@@ -1967,14 +1967,14 @@ dependencies = [
 
 [[package]]
 name = "wickra-c"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "wickra-core",
 ]
 
 [[package]]
 name = "wickra-core"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "approx",
  "proptest",
@@ -1984,7 +1984,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-data"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "approx",
  "csv",
@@ -2001,7 +2001,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-examples"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "serde_json",
  "tokio",
@@ -2011,7 +2011,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-node"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "napi",
  "napi-build",
@@ -2021,7 +2021,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-python"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "numpy",
  "pyo3",
@@ -2030,7 +2030,7 @@ dependencies = [
 
 [[package]]
 name = "wickra-wasm"
-version = "0.8.6"
+version = "0.8.7"
 dependencies = [
  "console_error_panic_hook",
  "js-sys",