fix: use JBANG_APP_* rather than JBANG_* for env config

[maxandersen]

This is mainly to see if removal of the 6+ year old sideffect found in #2341 actually breaks any tests.

[Copilot]

Pull request overview

This PR changes the environment variable prefix used to override directives in jbang scripts from JBANG_ to JBANG_APP_, addressing a 6+ year old naming collision issue. The change prevents accidental side effects where the JBANG_JAVA_OPTIONS environment variable (used by the jbang launcher script) would inadvertently override script directives.

Key Changes:

• Modified collectDirective() method to use JBANG_APP_ prefix instead of JBANG_ for directive environment variable overrides
• This affects directives like JAVA_OPTIONS, COMPILE_OPTIONS, RUNTIME_OPTIONS, etc.
• Breaking change: existing scripts relying on JBANG_<directive> env vars will need to switch to JBANG_APP_<directive>

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