Preserve "caused by" stack trace from caught errors

**Is your feature request related to a problem? Please describe.**

I have julia code which catches errors and adds context. For example:

```julia
d = Dict()
try
d["missing key"]
catch
error("Extra context information")
end
```

When the above code gets executed in native julia, it shows the error stack trace and the "caused by" stack trace i.e.

```
ERROR: Extra context information
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:35
[2] top-level scope
@ REPL[2]:4

caused by: KeyError: key "missing key" not found
Stacktrace:
[1] getindex(h::Dict{Any, Any}, key::String)
@ Base ./dict.jl:484
[2] top-level scope
@ REPL[2]:2
```

However, when I run the same code in pythoncall , the "caused by" trace is not shown:

```python
from juliacall import Main as jl
jl.seval("""
try
Dict()["missing key"]
catch
error("Extra context information")
end
""")
```

```
---------------------------------------------------------------------------
JuliaError Traceback (most recent call last)
Cell In[9], line 1
----> 1 jl.seval("""
2 try
3 Dict()["missing key"]
4 catch
5 error("Extra context information")
6 end
7 """)

File ~/.julia/packages/PythonCall/wXfah/src/jlwrap/module.jl:25, in seval(self, expr)
23 return ValueBase.__dir__(self) + self._jl_callmethod($(pyjl_methodnum(pyjlmodule_dir)))
24 def seval(self, expr):
---> 25 return self._jl_callmethod($(pyjl_methodnum(pyjlmodule_seval)), expr)
26 """, @__FILE__(), "exec"), jl.__dict__)
27 pycopy!(pyjlmoduletype, jl.ModuleValue)

JuliaError: Extra context information
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:35
[2] top-level scope
@ none:4
[3] eval
@ ./boot.jl:370 [inlined]
[4] eval
@ ./Base.jl:68 [inlined]
[5] pyjlmodule_seval(self::Module, expr::Py)
@ PythonCall ~/.julia/packages/PythonCall/wXfah/src/jlwrap/module.jl:13
[6] _pyjl_callmethod(f::Any, self_::Ptr{PythonCall.C.PyObject}, args_::Ptr{PythonCall.C.PyObject}, nargs::Int64)
@ PythonCall ~/.julia/packages/PythonCall/wXfah/src/jlwrap/base.jl:62
[7] _pyjl_callmethod(o::Ptr{PythonCall.C.PyObject}, args::Ptr{PythonCall.C.PyObject})
@ PythonCall.C ~/.julia/packages/PythonCall/wXfah/src/cpython/jlwrap.jl:47
```

Without this information, it is more difficult to tell what went wrong.

**Describe the solution you'd like**
Ideally, we would have the original stack trace shown below, e.g.

```
JuliaError: Extra context information
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:35
[2] top-level scope
@ none:4
[3] eval
@ ./boot.jl:370 [inlined]
[4] eval
@ ./Base.jl:68 [inlined]
[5] pyjlmodule_seval(self::Module, expr::Py)
@ PythonCall ~/.julia/packages/PythonCall/wXfah/src/jlwrap/module.jl:13
[6] _pyjl_callmethod(f::Any, self_::Ptr{PythonCall.C.PyObject}, args_::Ptr{PythonCall.C.PyObject}, nargs::Int64)
@ PythonCall ~/.julia/packages/PythonCall/wXfah/src/jlwrap/base.jl:62
[7] _pyjl_callmethod(o::Ptr{PythonCall.C.PyObject}, args::Ptr{PythonCall.C.PyObject})
@ PythonCall.C ~/.julia/packages/PythonCall/wXfah/src/cpython/jlwrap.jl:47

caused by: KeyError: key "missing key" not found
Stacktrace:
[1] getindex(h::Dict{Any, Any}, key::String)
@ Base ./dict.jl:484
[2] top-level scope
@ REPL[2]:2
```

Reproduce the behavior through jl.seval and begin with the PythonCall stack frames shown in src/jlwrap/module.jl:25 and src/jlwrap/module.jl:13. Trace how the caught Julia error becomes JuliaError, then verify that the original caused-by message and stack trace are preserved in the rendered exception.

索引モデルが issue の本文から書いたものです。