feat: restore vendored pcre option

[freedmand]

Description

Fixes #44. Adds an option to use the vendored pcre that defaults to true. For installation with package managers like Homebrew, vendored_pcre will be set to false to use the included package.

Test Steps

These commands all work as expected:

• zig build
• zig build -Dvendored-pcre=true
• zig build -Dvendored-pcre=false (ensure you have installed pcre on the system, e.g. brew install pcre)