chore: upgrade Fable and fable-library to 5.8.0 (#347)

Fable 5.7 introduced a hard coupling between the Fable compiler and the
fable-library runtime: fable-library 5.6 no longer works with Fable 5.7+,
so the compiler tool and the Python runtime must be bumped together.

Upgrade both in lockstep to 5.8.0:
- .config/dotnet-tools.json: Fable CLI 5.6.0 -> 5.8.0
- pyproject.toml: fable-library==5.6.0 -> ==5.8.0
- uv.lock: regenerated

All 563 tests pass with the matched 5.8.0 toolchain.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dbrattli

.config/dotnet-tools.json

@@ -10,7 +10,7 @@
       "rollForward": false
     },
     "fable": {
-      "version": "5.6.0",
+      "version": "5.8.0",
       "commands": [
         "fable"
       ],

pyproject.toml

@@ -7,7 +7,7 @@ requires-python = ">= 3.12, < 4"
 readme = "README.md"
 license = "MIT"
 dependencies = [
-    "fable-library==5.6.0",
+    "fable-library==5.8.0",
     "pyright>=1.1.411",
 ]