fix: raise minimum Elixir to 1.19, use PCRE2-standard \p{Xan}

The dependency chain (ex_ast via reach) already requires Elixir ~> 1.19,
so the advertised ~> 1.16 was wrong; the CI matrix now tests 1.19/OTP 26
and 1.20/OTP 27. is_alphanumeric used \p{Alphabetic}, which PCRE2 only
gained in recent OTP releases and failed to compile on OTP 27; \p{Xan}
is the long-standing standard property for letters and numbers.

Author: gilbertwong96

.github/workflows/ci.yml

@@ -15,9 +15,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - elixir: "1.16"
+          - elixir: "1.19"
             otp: "26"
-          - elixir: "1.18"
+          - elixir: "1.20"
             otp: "27"
     steps:
       - uses: actions/checkout@v4
@@ -56,7 +56,7 @@ jobs:
 
       - uses: erlef/setup-beam@v1
         with:
-          elixir-version: "1.18"
+          elixir-version: "1.20"
           otp-version: "27"
 
       - uses: actions/cache@v4

lib/lovely_mermaid/labels.ex

@@ -92,7 +92,7 @@ defmodule LovelyMermaid.Labels do
 
   @doc "Matches Rust's `char::is_alphanumeric`."
   @spec is_alphanumeric(String.t()) :: boolean()
-  def is_alphanumeric(c), do: String.match?(c, ~r/[\p{Alphabetic}\p{N}]/u)
+  def is_alphanumeric(c), do: String.match?(c, ~r/[\p{Xan}]/u)
 
   @doc "Characters allowed in a bare node/state/class identifier."
   @spec is_id_char(String.t()) :: boolean()

mix.exs

@@ -8,7 +8,7 @@ defmodule LovelyMermaid.MixProject do
     [
       app: :lovely_mermaid,
       version: @version,
-      elixir: "~> 1.16",
+      elixir: "~> 1.19",
       start_permanent: Mix.env() == :prod,
       deps: deps(),
       aliases: aliases(),