refactor: migrate shiki to core API with dynamic language/theme loading

- Update code block regex to support symbols/numbers in language identifiers
- Adjust codespan background color to a softer shade

src/render/codeToANSI.ts

@@ -24,7 +24,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE. */
 
 import c from "chalk";
-import type { BundledLanguage, BundledTheme, HighlighterGeneric } from "shiki";
+import type { BundledLanguage, BundledTheme, HighlighterCore } from "shiki";
 
 // From @shikijs/vscode-textmate
 enum FontStyle {
@@ -37,7 +37,7 @@ enum FontStyle {
 }
 
 export function codeToANSI(
-  highlighter: HighlighterGeneric<BundledLanguage, BundledTheme>,
+  highlighter: HighlighterCore,
   code: string,
   lang: BundledLanguage,
   theme: BundledTheme,