Improve activation script resiliency

This way, it doesn't mess with the `curr_dir` in the `sbatch` script but
doesn't require a directory stack, all while not being influenced by
outside variables.

pytorch-ddp-example/activate.sh

 #!/usr/bin/env bash
 
-if [ -z "$curr_dir" ]; then
-    curr_file="${BASH_SOURCE[0]:-${(%):-%x}}"
-    curr_dir="$(dirname "$curr_file")"
-fi
+_curr_file="${BASH_SOURCE[0]:-${(%):-%x}}"
+_curr_dir="$(dirname "$_curr_file")"
 
-venv_dir="$curr_dir"/env-"$SYSTEMNAME"
+venv_dir="$_curr_dir"/env-"$SYSTEMNAME"
 
 [ "$(command -v deactivate)" ] && deactivate
 
 module --force purge
-if ! [ -f "$curr_dir"/modules.sh ]; then
-    echo "Cannot find \`$curr_dir/modules.sh\`; its existence is required."
+if ! [ -f "$_curr_dir"/modules.sh ]; then
+    echo "Cannot find \`$_curr_dir/modules.sh\`; its existence is required."
     return 1
 fi
-source "$curr_dir"/modules.sh
+source "$_curr_dir"/modules.sh
 
 if ! [ -d "$venv_dir" ]; then
-    echo "Please manually execute \`nice bash ${curr_dir@Q}/set_up.sh\`" \
+    echo "Please manually execute \`nice bash ${_curr_dir@Q}/set_up.sh\`" \
          "on a login node to create the \`venv\`."
     return 1
 elif ! [ -f "$venv_dir"/bin/activate ]; then
     echo "Something seems to be wrong with the \`venv\` at \`$venv_dir\`." \
          "Please delete it (\`nice rm -rf ${venv_dir@Q}\`) and" \
-         "execute \`nice bash ${curr_dir@Q}/set_up.sh\`" \
+         "execute \`nice bash ${_curr_dir@Q}/set_up.sh\`" \
          "on a login node to re-create the \`venv\`."
     return 1
 fi

pytorch-fsdp-example/activate.sh

 #!/usr/bin/env bash
 
-if [ -z "$curr_dir" ]; then
-    curr_file="${BASH_SOURCE[0]:-${(%):-%x}}"
-    curr_dir="$(dirname "$curr_file")"
-fi
+_curr_file="${BASH_SOURCE[0]:-${(%):-%x}}"
+_curr_dir="$(dirname "$_curr_file")"
 
-venv_dir="$curr_dir"/env-"$SYSTEMNAME"
+venv_dir="$_curr_dir"/env-"$SYSTEMNAME"
 
 [ "$(command -v deactivate)" ] && deactivate
 
 module --force purge
-if ! [ -f "$curr_dir"/modules.sh ]; then
-    echo "Cannot find \`$curr_dir/modules.sh\`; its existence is required."
+if ! [ -f "$_curr_dir"/modules.sh ]; then
+    echo "Cannot find \`$_curr_dir/modules.sh\`; its existence is required."
     return 1
 fi
-source "$curr_dir"/modules.sh
+source "$_curr_dir"/modules.sh
 
 if ! [ -d "$venv_dir" ]; then
-    echo "Please manually execute \`nice bash ${curr_dir@Q}/set_up.sh\`" \
+    echo "Please manually execute \`nice bash ${_curr_dir@Q}/set_up.sh\`" \
          "on a login node to create the \`venv\`."
     return 1
 elif ! [ -f "$venv_dir"/bin/activate ]; then
     echo "Something seems to be wrong with the \`venv\` at \`$venv_dir\`." \
          "Please delete it (\`nice rm -rf ${venv_dir@Q}\`) and" \
-         "execute \`nice bash ${curr_dir@Q}/set_up.sh\`" \
+         "execute \`nice bash ${_curr_dir@Q}/set_up.sh\`" \
          "on a login node to re-create the \`venv\`."
     return 1
 fi