Emojis in grammar causes crash

# Prerequisites

Please answer the following questions for yourself before submitting an issue.

- [X] I am running the latest code. Development is very rapid so there are no tagged versions as of now.
- [X] I carefully followed the [README.md](https://github.com/abetlen/llama-cpp-python/blob/main/README.md).
- [X] I [searched using keywords relevant to my issue](https://docs.github.com/en/issues/tracking-your-work-with-issues/filtering-and-searching-issues-and-pull-requests) to make sure that I am creating a new issue that is not already open (or closed).
- [X] I reviewed the [Discussions](https://github.com/abetlen/llama-cpp-python/discussions), and have a new bug or useful enhancement to share.

# Expected Behavior

When using emojis in grammar, I expect the grammar to work the same way as in `llama.cpp` .
Here's an example of grammar that works in `llama.cpp`, but not `llama-cpp-python`:
```
root ::= emoji+
emoji ::= [😀-🙏]
```

# Current Behavior

`llama-cpp-python` is unable to parse the emojis and instead crashes.

# Environment and Context

* Physical (or virtual) hardware you are using, e.g. for Linux:

```
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Address sizes: 48 bits physical, 48 bits virtual
Byte Order: Little Endian
CPU(s): 24
On-line CPU(s) list: 0-23
Vendor ID: AuthenticAMD
Model name: AMD Ryzen 9 5900X 12-Core Processor
CPU family: 25
Model: 33
Thread(s) per core: 2
Core(s) per socket: 12
Socket(s): 1
Stepping: 2
BogoMIPS: 7400.07
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx m
mxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl tsc_reliable nonstop_tsc cpuid extd_apicid pni pclmul
qdq ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm cmp_legacy svm cr8_leg
acy abm sse4a misalignsse 3dnowprefetch osvw topoext perfctr_core ssbd ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2
smep bmi2 erms invpcid rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves clzero xsaveerptr a
rat npt nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold v_vmsave_vmload umip vae
s vpclmulqdq rdpid fsrm
Virtualization features:
Virtualization: AMD-V
Hypervisor vendor: Microsoft
Virtualization type: full
Caches (sum of all):
L1d: 384 KiB (12 instances)
L1i: 384 KiB (12 instances)
L2: 6 MiB (12 instances)
L3: 32 MiB (1 instance)
Vulnerabilities:
Gather data sampling: Not affected
Itlb multihit: Not affected
L1tf: Not affected
Mds: Not affected
Meltdown: Not affected
Mmio stale data: Not affected
Retbleed: Not affected
Spec rstack overflow: Mitigation; safe RET, no microcode
Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp
Spectre v1: Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Spectre v2: Mitigation; Retpolines, IBPB conditional, IBRS_FW, STIBP conditional, RSB filling, PBRSB-eIBRS Not affected
Srbds: Not affected
Tsx async abort: Not affected
```

* Operating System, e.g. for Linux:

```
Linux DESKTOP-P7EJA62 5.15.133.1-microsoft-standard-WSL2 #1 SMP Thu Oct 5 21:02:42 UTC 2023 x86_64 GNU/Linux
```

* SDK version, e.g. for Linux:

```
Python 3.11.2
GNU Make 4.3
g++ (Debian 12.2.0-14) 12.2.0
```

# Failure Information (for bugs)

This issue seems to be the same as https://github.com/ggerganov/llama.cpp/issues/2501

# Steps to Reproduce

Here's a short Python snippet that reproduces the issue:
```
from llama_cpp import LlamaGrammar

grammar = '''
root ::= emoji+
emoji ::= [😀-🙏]
'''

LlamaGrammar.from_string(grammar)
```

# Failure Logs

```
Traceback (most recent call last):
File "/home/username/documents/heggiz/worker-llama-cpp/repro.py", line 8, in
LlamaGrammar.from_string(grammar)
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 68, in from_string
parsed_grammar = parse(const_char_p(grammar)) # type: parse_state
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 1013, in parse
pos = parse_rule(state, pos)
^^^^^^^^^^^^^^^^^^^^^^
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 984, in parse_rule
pos = parse_alternates(state, pos, name, rule_id, False) # type: const_char_p
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 939, in parse_alternates
pos = parse_sequence(state, src, rule_name, rule, is_nested) # type: const_char_p
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 774, in parse_sequence
char_pair = parse_char(pos) # type: Tuple[int, const_char_p]
^^^^^^^^^^^^^^^
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 664, in parse_char
return decode_utf8(src)
^^^^^^^^^^^^^^^^
File "/home/username/documents/heggiz/worker-llama-cpp/venv/lib/python3.11/site-packages/llama_cpp/llama_grammar.py", line 561, in decode_utf8
len = lookup[highbits] # type: int
~~~~~~^^^^^^^^^^
IndexError: tuple index out of range
```