Fix neovim symlink target: was basename(tarball), now explicit NVIM_EXTRACT_DIR

The tarball filename is nvim-linux-arm64.tar.gz but the extracted
directory inside it is also named nvim-linux-arm64. However, my
original code did $(basename nvim.tar.gz .tar.gz) which returns 'nvim'
(strips both the directory and the suffix), creating a symlink to
/opt/nvim/bin/nvim that pointed to a non-existent path.

Discovered on rye after the bootstrap appeared to succeed but nvim
wasn't findable. Fixed by hardcoding the extracted directory name
based on the arch case:

  x86_64:   nvim-linux64.tar.gz  ->  nvim-linux64
  aarch64:  nvim-linux-arm64.tar.gz -> nvim-linux-arm64

Same fix applied to:
- run_once_20-install-user-packages.sh.tmpl (initial install)
- dot_local/bin/update-neovim.sh (topgrade-time updates)

Verified on rye: /usr/local/bin/nvim -> /opt/nvim-linux-arm64/bin/nvim,
'nvim --version' returns 'NVIM v0.11.4'.

dot_local/bin/update-neovim.sh

@@ -14,8 +14,14 @@ NVIM_TARGET_VERSION="v0.11.4"
 
 ARCH="$(uname -m)"
 case "$ARCH" in
-    x86_64)        NVIM_TARBALL="nvim-linux64.tar.gz" ;;
-    aarch64|arm64) NVIM_TARBALL="nvim-linux-arm64.tar.gz" ;;
+    x86_64)
+        NVIM_TARBALL="nvim-linux64.tar.gz"
+        NVIM_EXTRACT_DIR="nvim-linux64"
+        ;;
+    aarch64|arm64)
+        NVIM_TARBALL="nvim-linux-arm64.tar.gz"
+        NVIM_EXTRACT_DIR="nvim-linux-arm64"
+        ;;
     *)
         echo "unsupported arch: $ARCH" >&2
         exit 1
@@ -46,7 +52,7 @@ fi
 
 sudo rm -rf /opt/nvim-linux* /usr/local/bin/nvim
 sudo tar -xzf "$TMP_TARBALL" -C /opt/
-sudo ln -sf "/opt/$(basename "$TMP_TARBALL" .tar.gz)/bin/nvim" /usr/local/bin/nvim
+sudo ln -sf "/opt/${NVIM_EXTRACT_DIR}/bin/nvim" /usr/local/bin/nvim
 
 echo "neovim $NVIM_TARGET_VERSION installed"
 nvim --version | head -1

run_once_20-install-user-packages.sh.tmpl

@@ -68,8 +68,14 @@ fi
 NVIM_TARGET_VERSION="v0.11.4"
 ARCH="$(uname -m)"
 case "$ARCH" in
-    x86_64)        NVIM_TARBALL="nvim-linux64.tar.gz" ;;
-    aarch64|arm64) NVIM_TARBALL="nvim-linux-arm64.tar.gz" ;;
+    x86_64)
+        NVIM_TARBALL="nvim-linux64.tar.gz"
+        NVIM_EXTRACT_DIR="nvim-linux64"
+        ;;
+    aarch64|arm64)
+        NVIM_TARBALL="nvim-linux-arm64.tar.gz"
+        NVIM_EXTRACT_DIR="nvim-linux-arm64"
+        ;;
     *)
         die "unsupported arch for neovim tarball: $ARCH"
         ;;
@@ -95,7 +101,7 @@ if [[ -n "$NVIM_TARBALL" ]]; then
     fi
     sudo rm -rf /opt/nvim-linux* /usr/local/bin/nvim
     sudo tar -xzf nvim.tar.gz -C /opt/
-    sudo ln -sf "/opt/$(basename nvim.tar.gz .tar.gz)/bin/nvim" /usr/local/bin/nvim
+    sudo ln -sf "/opt/${NVIM_EXTRACT_DIR}/bin/nvim" /usr/local/bin/nvim
     rm -f nvim.tar.gz
 fi