Refactor write_view_segment in MDL writer to reduce parameter count

[bpowers]

Description

The write_view_segment function in src/simlin-engine/src/mdl/writer.rs takes 8 parameters, which triggers clippy's too_many_arguments lint. The lint is currently suppressed with #[allow(clippy::too_many_arguments)].

Several of the parameters represent shared context that is threaded through the function: valve_uids, elem_positions, name_map, next_connector_uid, etc. These should be grouped into a context struct (e.g., ViewWriteContext) to improve readability and reduce the function signature size.

Why it matters

• Maintainability: Long parameter lists make it harder to understand what the function needs and easier to mix up arguments at call sites.
• Clippy compliance: Suppressing lints with #[allow(...)] should be a last resort, not a permanent fixture. Reducing the parameter count removes the need for the suppression.
• Developer experience: A context struct makes it clearer which pieces of state are related and passed together.

Component(s) affected

• src/simlin-engine/src/mdl/writer.rs -- the write_view_segment function

Possible approach

Introduce a struct (e.g., ViewWriteContext) that bundles the shared parameters:

• valve_uids
• elem_positions
• name_map
• next_connector_uid
• any other context that is passed through multiple writer functions

Then replace the individual parameters with a single &mut ViewWriteContext reference.

Context

Identified during review of PR #397 (mdl-roundtrip-fidelity branch). This is a code quality improvement that does not affect correctness.