fix(itkwasm): support the wasmtime-py 48 preopen_dir signature

[thewtex]

Problem

wasmtime-py 48.0.0 removed the DirPerms and FilePerms enums and changed the
WasiConfig.preopen_dir signature:

wasmtime-py	signature	exports DirPerms / FilePerms
28.0.0 – 47.x	preopen_dir(path, guest_path, dir_perms=DirPerms.READ_WRITE, file_perms=FilePerms.READ_WRITE)	yes
48.0.0	preopen_dir(path, guest_path, fs_mutable=True)	no

itkwasm/pipeline.py imported both names at module scope, inside the
if sys.platform != "emscripten": block. So on wasmtime-py 48 the failure was not
limited to pipelines that perform file I/O — plain import itkwasm raised
ImportError, breaking the package for every user who picked up the new wasmtime.

Changes

Drop the two imports and pass only the path arguments:

for preopen in preopen_directories:
    wasi_config.preopen_dir(preopen, preopen)

Read-write is the default on both sides of the break — DirPerms.READ_WRITE /
FilePerms.READ_WRITE on ≤ 47, fs_mutable=True on 48 — so the two-argument call is
semantically identical across the whole supported range. That means no conditional
import, no try/except ImportError shim, and no version-sniffing branch; it also
keeps the existing wasmtime >= 28.0.0 floor in pyproject.toml valid, so no
dependency bound needed changing.

Every other wasmtime API this module touches was checked against 48.0.0 and is
unchanged: the nine Config feature flags (wasm_bulk_memory, wasm_simd,
wasm_relaxed_simd, wasm_relaxed_simd_deterministic, wasm_memory64,
cranelift_opt_level, strategy, cache, parallel_compilation),
WasiConfig.inherit_* / argv, Module.deserialize_file, and Linker.define_wasi.
DirPerms / FilePerms were the only casualties.

Test coverage

The changed lines were already executed by the existing suite, but line coverage was
misleading here. In test_pipeline_input_output_files the inputs live in
test/input/ and the outputs in a temporary directory, so the run produces two
preopens, each exercised read-only or write-only. The case where a single
preopen must serve both reads and writes — precisely the read-write default this fix
now leans on — had no coverage.

test_pipeline_input_output_files_same_directory closes that gap: it copies both
inputs into the temp directory so preopen_directories collapses to one entry that
has to handle reads and writes at once. It carries the same win32 skipif as its
sibling test.

To confirm the new test is not vacuous, the preopen was temporarily mutated to
read-only (preopen_dir(preopen, preopen, False)); both file tests then fail with
Could not open outputTxtFile., so the test genuinely pins the semantics rather than
passing by construction.

Verification

packages/core/python/itkwasm/test/test_pipeline.py was run against both ends of the
supported range, in isolated environments:

• wasmtime-py 28.0.0 (dependency floor) — import itkwasm OK, 11 passed
• wasmtime-py 48.0.0 (the breaking release) — import itkwasm OK, 11 passed

test_pipeline_dask_array_input was deselected in both local runs because dask is
absent from the minimal verification venvs; it is unrelated to this change and CI
runs it via the full pixi environment.

CodeRabbit review on the diff returned 0 findings.

Notes for reviewers

• This branch also contains a separate chore commit bumping __version__
  from 1.0b200 to 1.0b201, so the fix can ship to PyPI.
• No documentation updates were needed: neither AGENTS.md, the root README.md,
  nor packages/core/python/itkwasm/README.md documents wasmtime version
  constraints, and this change alters no public API, environment variable, or
  developer workflow.
• black --check reports pipeline.py as unformatted, but it does so on the
  unmodified file at main as well (pre-existing trailing whitespace elsewhere in
  the file), and the black diff does not touch the changed region. Left alone here
  to keep this fix's diff small.

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