Wasm file resolution bug

[qartik]

Following #1339 and subsequent release of guppy v0.21.7, there's a regression in wasm file path resolution.

If I have my file structure as follows:

❯ tree
.
├── guppy_wasm.ipynb
└── wasm
    ├── arith.wasm
    └── wasm.py

and wasm.py has:

@wasm_module("arith.wasm")
class MyWasm:
    @wasm
    def add(self: "MyWasm", a: int, b: int) -> int: ...
[...]
@guppy
def main() -> None:

    [mod1] = spawn_wasm_contexts(1, MyWasm)
    res5 = mod1.add(10, 32)
[...]

Then if I do from wasm.wasm import main from guppy_wasm.ipynb, I get:

---------------------------------------------------------------------------
GuppyError                                Traceback (most recent call last)
Cell In[1], [line 3](vscode-notebook-cell:?execution_count=1&line=3)
      1 import qnexus as qnx
      2 from rich import print as rprint
----> [3](vscode-notebook-cell:?execution_count=1&line=3) from wasm.wasm import main

File ~/GH/qapi-submit/wasm/wasm.py:10
      6 from guppylang.std.qsystem.wasm import spawn_wasm_contexts
      7 from guppylang_internals.decorator import wasm, wasm_module
---> [10](~/GH/qapi-submit/wasm/wasm.py:10) @wasm_module("arith.wasm")
     11 class MyWasm:
     12     @wasm
     13     def add(self: "MyWasm", a: int, b: int) -> int: ...

File ~/GH/qapi-submit/.venv/lib/python3.13/site-packages/guppylang_internals/decorator.py:217, in wasm_module(filename)
    215     wasm_sigs = decode_wasm_functions(filename)
    216 else:
--> [217](~/GH/qapi-submit/.venv/lib/python3.13/site-packages/guppylang_internals/decorator.py:217)     raise GuppyError(WasmFileNotFound(None, filename))
    219 def type_def_wrapper(
    220     id: DefId,
    221     name: str,
   (...)    224     config: str | None,
    225 ) -> OpaqueTypeDef:
    226     assert config is None

GuppyError: WasmFileNotFound(span=None, _parent=None, children=[], file='arith.wasm')

Changing the file path in the decorate to @wasm_module("wasm/arith.wasm") works.

We should be looking at the relative path from the guppy source, not the execution site.