Bump version to 1.3.0 in gleam.toml

Update the project version from 1.2.3 to 1.3.0 in preparation for a new release.

Author: lupodevelop

gleam.toml

@@ -1,5 +1,5 @@
 name = "str"
-version = "1.2.3"
+version = "1.3.0"
 
 # Project metadata (fill or replace placeholders before publishing)
 description = "Unicode-aware string utilities for Gleam: grapheme-safe operations, pragmatic ASCII transliteration, and slug generation."