use Files.createTempFile for owner-only groovysh/groovyc temp files

[netliomax25-code]

1. groovysh /less and /nano write the interactive session buffer to a temp file created with java.io.File.createTempFile, which under a typical umask (022) is created world-readable (rw-r--r--). The buffer often holds connection strings, tokens, or credentials the user has typed.
2. Groovyc.addSourceFiles writes the forked compilers source-file list to a temp file the same way when the command line exceeds the Windows length limit.
3. On a shared host any other local user can then read these artifacts. This is the same CWE-377/378 class already addressed for temp directories by moving to NIO (the CVE-2020-17521 fix, listed as property P4 in THREAT_MODEL.md), but these temp files were still using the java.io API.

Switched the three sites to java.nio.file.Files.createTempFile(...).toFile(), which yields owner-only (rw-------) permissions on POSIX. Behavior for the owning user is unchanged; the forked compiler and the jline pager run as the same user, so the tighter mode does not affect them.

Verified locally that java.io.File.createTempFile produces rw-r--r-- under umask 022 while Files.createTempFile produces rw-------; the two modules compile cleanly.

[testlens-app]

✅ All tests passed ✅

🏷️ Commit: 859178d
▶️ Tests: 102571 executed
⚪️ Checks: 23/23 completed

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[paulk-asert]

Merged. Thanks!