MNT: Adjust `fslStartup` test to support micromamba-based installations

unit_tests/utils/feedsRun.fslStartup

 #!/usr/bin/env fslpython
 
-#Note this script requires a conda activate script to be on the PATH
+# Note this script attempts to activate the $FSLDIR conda environment in
+# order to compile the test_fslStartup.cc program. Therefore this script
+# expects one of the following to be true:
+#
+#   - A $FSLDIR/bin/activate script to be present
+#   - A $FSLDIR/bin/micromamba executable to be present
+#
 
 import os
+import os.path as op
 import shlex
 import sys
 import tempfile
@@ -35,22 +42,38 @@ def run(cmd, ompthreads=None, blasthreads=None, fslskipglobal=None):
     return result.stdout.strip().split('\n')[-1]
 
 
-def main():
-    env = os.environ.copy()
-    activatePath = Path(f'''{env['FSLDIR']}/bin/activate''')
-    if not activatePath.is_file():
-       activatePath='activate'
+def genActivateCommand():
+
+    fsldir   = os.environ['FSLDIR']
+    mmbin    = f'{fsldir}/bin/micromamba'
+    activate = f'{fsldir}/bin/activate'
+
+    if op.exists(mmbin):
+        return '; '.join([
+            f'eval $({mmbin} shell hook --shell posix)',
+            f'micromamba activate {fsldir}'])
 
-    outdir        = Path(sys.argv[1])
+    elif op.exists(activate):
+        return f'source {activate} {fsldir}'
 
-    buildcmds = [f'''source {activatePath} $FSLDIR''',
-                 'source $FSLDIR/etc/fslconf/fsl-devel.sh',
-		 f'''cp Makefile test_fslStartup.cc {outdir}''',
-		 f'''cd {outdir}''',
-                 'make']
+    # hope that there's an activate script/func available
+    else:
+        return f'source activate {fsldir}'
+
+
+def main():
+    fsldir = os.environ['FSLDIR']
+    outdir = Path(sys.argv[1])
+
+    buildcmds = [
+        genActivateCommand(),
+        f'source {fsldir}/etc/fslconf/fsl-devel.sh',
+        f'cp Makefile test_fslStartup.cc {outdir}',
+        f'cd {outdir}',
+        'make']
     sp.run('; '.join(buildcmds), check=True, shell=True)
 
-    os.chdir(outdir)    
+    os.chdir(outdir)
 
     # Default behaviour should be: OMP multi-threaded, BLAS single threaded.
     assert run('./test_fslStartup', 8, 8) == '8 1 8'