Make (gmeep) s-parameter caching more stable

[gronniger]

Currently, metadata generated by kfactory in the GDS file used to hash the simulated component can cause cache miss when changing gdsfactory or kfactory version or changing order of certain operations (which change neither component nor GDS shapes).
With this PR, metadata is not written to GDS for hashing, so caching should be more stable.
This is tested for gmeep, but should work the same for other simulation tools.

Summary by Sourcery

Stabilize s-parameter caching by ensuring component GDS exports used for hashing are written without extraneous metadata and consistently handled paths.

Enhancements:

• Export component GDS files for hashing without metadata and empty cells to make s-parameter cache keys independent of non-geometric changes.
• Standardize path handling in s-parameter path utilities by using the Path alias consistently.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adjusts how component GDS files are written and paths handled so that s-parameter caching ignores kfactory/gdsfactory metadata and uses more stable hashing, while also standardizing path handling via pathlib.Path imports.

Sequence diagram for stable sparameter caching via GDS hashing

sequenceDiagram
    actor User
    participant Caller as caller_module
    participant GetPath as _get_sparameters_path
    participant Gf as gf
    participant Comp as Component
    participant Hash as get_component_hash
    participant FS as filesystem

    User->>Caller: request_sparameters(component, **kwargs)
    Caller->>GetPath: _get_sparameters_path(component, dirpath, **kwargs)
    GetPath->>Gf: get_component(component)
    Gf-->>GetPath: Component instance
    GetPath->>Hash: get_component_hash(component)

    activate Hash
    Hash->>Comp: write_gds(no_empty_cells=True, with_metadata=False)
    Comp-->>Hash: gdspath
    Hash->>FS: read_bytes(gdspath)
    FS-->>Hash: gds_bytes
    Hash->>Hash: md5(gds_bytes)
    Hash->>FS: unlink(gdspath)
    Hash-->>GetPath: component_hash
    deactivate Hash

    GetPath->>GetPath: dirpath = Path(dirpath)
    GetPath->>GetPath: dirpath = dirpath / component.name
    GetPath-->>Caller: sparameters_path
    Caller-->>User: return cached_or_computed_sparameters

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Flow diagram for get_component_hash using metadatafree GDS

flowchart TD
    A["get_component_hash(component)"] --> B["call component.write_gds(no_empty_cells=True, with_metadata=False)"]
    B --> C["receive gdspath string"]
    C --> D["convert to Path(gdspath)"]
    D --> E["read_bytes() from GDS file"]
    E --> F["compute md5 hash of bytes"]
    F --> G["unlink() temporary GDS file"]
    G --> H["return hash string"]

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File-Level Changes

Change	Details	Files
Make component GDS hashing stable by excluding metadata and empty cells from the temporary GDS used for the hash.	Change temporary GDS write call to pass no_empty_cells=True so empty cells are omitted from the hash input GDS. Disable metadata writing in the temporary GDS used for hashing by passing with_metadata=False. Continue hashing the temporary GDS file via its MD5 and deleting it afterwards to avoid leaving artifacts.	gplugins/common/utils/get_sparameters_path.py
Standardize path handling in s-parameter path computation using direct Path imports instead of pathlib.Path.	Replace pathlib.Path calls with Path to match the existing Path import style. Normalize dirpath handling by wrapping provided or default directory strings with Path consistently before use.	gplugins/common/utils/get_sparameters_path.py

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[sourcery-ai]

Hey - I've left some high level feedback:

• You still convert dirpath to a Path twice in _get_sparameters_path; consider doing this once near the top of the function to avoid redundant work and keep the logic clearer.
• In get_component_hash, you might consider using a context-managed temporary file (e.g., tempfile.NamedTemporaryFile) or an in-memory GDS export if available, to avoid relying on manual deletion and make the cleanup more robust.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- You still convert `dirpath` to a `Path` twice in `_get_sparameters_path`; consider doing this once near the top of the function to avoid redundant work and keep the logic clearer.
- In `get_component_hash`, you might consider using a context-managed temporary file (e.g., `tempfile.NamedTemporaryFile`) or an in-memory GDS export if available, to avoid relying on manual deletion and make the cleanup more robust.

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