vocab : add special infill tokens for CodeLlama

The commit adds the following special tokens for CodeLlama infill:
- ▁<PRE>
- ▁<SUF>
- ▁<MID>

The motivation for this is that currently the infill example uses
CodeLlama as a suggested model. But when using this model the following
error is generated:
```console
/llama.cpp-debug/examples/infill/infill.cpp:165: GGML_ASSERT(llama_vocab_fim_pre(vocab) >= 0) failed

Could not attach to process.  If your uid matches the uid of the target
process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operation not permitted.
No stack.
The program is not being run.
305251 Aborted                 (core dumped)
./build/bin/llama-infill -t 10 -ngl 0 -m models/codellama-13b.Q5_K_S.gguf \
  -c 4096 --temp 0.7 --repeat_penalty 1.1 -n 20 \
  --in-prefix "def helloworld():\n    print(\"hell" \
  --in-suffix "\n   print(\"goodbye world\")\n    "
```

src/llama-vocab.cpp

@@ -1801,6 +1801,7 @@ void llama_vocab::impl::load(llama_model_loader & ml, const LLM_KV & kv) {
                         || t.first == "<fim-prefix>"
                         || t.first == "<｜fim▁begin｜>" // DeepSeek
                         || t.first == "<PRE>"
+                        || t.first == "▁<PRE>"          // CodeLlama
                         ) {
                     special_fim_pre_id = t.second;
                     if ((id_to_token[t.second].attr & LLAMA_TOKEN_ATTR_CONTROL) == 0) {
@@ -1818,6 +1819,7 @@ void llama_vocab::impl::load(llama_model_loader & ml, const LLM_KV & kv) {
                         || t.first == "<fim-suffix>"
                         || t.first == "<｜fim▁hole｜>" // DeepSeek
                         || t.first == "<SUF>"
+                        || t.first == "▁<SUF>"         // CodeLlama
                         ) {
                     special_fim_suf_id = t.second;
                     if ((id_to_token[t.second].attr & LLAMA_TOKEN_ATTR_CONTROL) == 0) {
@@ -1835,6 +1837,7 @@ void llama_vocab::impl::load(llama_model_loader & ml, const LLM_KV & kv) {
                         || t.first == "<fim-middle>"
                         || t.first == "<｜fim▁end｜>"  // DeepSeek
                         || t.first == "<MID>"
+                        || t.first == "▁<MID>"         // CodeLlama
                         ) {
                     special_fim_mid_id = t.second;
                     if ((id_to_token[t.second].attr & LLAMA_TOKEN_ATTR_CONTROL) == 0) {