Reading from arguments doesn't work with bpftrace

```julia
julia> using UProbes

julia> function f(arg)
if @query(:julia, :test, typeof(arg))
@probe(:julia, :test, arg)
end
end
f (generic function with 1 method)

julia> while true
i = rand(Int64)
f(i)
end
```

```
➜ ~ sudo bpftrace -p 31417 -e "usdt:julia:test { @[comm] = hist(arg0); }"
Attaching 1 probe...
Code not generated for probe: usdt:/tmp/jl_bnvl90:test
```

```
➜ ~ readelf -n /tmp/jl_bnvl90

Displaying notes found in: .note.stapsdt
Owner Data size Description
stapsdt 0x0000002f NT_STAPSDT (SystemTap probe descriptors)
Provider: julia
Name: test
Location: 0x0000000000001005, Base: 0x0000000000002000, Semaphore: 0x0000000000004000
Arguments: -8@-8(%rsp)
```

Reproduce the Julia example using UProbes, then run the shown bpftrace command and inspect the generated probe descriptor with readelf -n. Start by tracing how @probe emits the STAPSDT Arguments entry; done means bpftrace attaches successfully and can read the emitted argument value.

Written by the indexing model from the issue text.