lsame: simplify using IACHAR

[jschueller]

Replace ICHAR with the F95 intrinsic IACHAR, which always returns ASCII codes regardless of the platform's native character encoding. This eliminates the entire EBCDIC/Prime machine detection branch (logic testing ZCODE against ASCII/EBCDIC/Prime codes), producing shorter, simpler, and equivalent code.

Closes #701

[ACSimon33]

We might want to change the file extension to .f95 to make the required standard explicit. We did that for some new routines with .f90.

[jschueller]

ah, yes, I did not get that, are we allowed to use f95 in lapack though ?

[langou]

(1) I'd be OK to allow F95
(2) if we do F95, it would be good practice to indicate it in the file name as suggested by @ACSimon33
(3) in the past, I would have argued to move the current lsame.f to the "deprecated" folder, but I guess that's why we have source control so I think changing lsame.f and not keeping an older version is just fine.

More comments on the wisdom to allow F95 welcome.

[imciner2]

We might want to change the file extension to .f95 to make the required standard explicit. We did that for some new routines with .f90.

Please don't use .f95 extensions to mean Fortran 95 code, keep the separation .f for fixed form and .f90 for free-form. Some compilers (such as the Intel one), don't recognize any file extension other than .f or .f90 without special command line options (https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2026-0/file-extensions.html), and the usual advice has been to not use any other extensions (https://stevelionel.com/drfortran/2013/01/11/doctor-fortran-in-source-form-just-wants-to-be-free/).