devel/libchdr: Update to g20260310

• Use short hash for GH_TAGNAME. This follows the Porter's Handbook more closely.
• Split Github variables into separate section for improved readability.
• Add option LTO, enabled by default. This replaces enabling LTO via the WITH_LTO variable. Having an LTO port option is more commonly used in the ports tree.
• Replace zlib with miniz in EXTRACT_AFTER_ARGS because upstream has switched to a leaner implementation for the vendored zlib. Also safeguard every --exclude entry to match the intended path only and place them on a separate line for improved readability.

Changelog: https://github.com/rtissera/libchdr/compare/40f96ee...7715de1

PR: 294074