Refactor chain to use a vec

[christian-schilling]

It was discovered during profiling that filter optimisation spends lots of time rearranging chains.
Using a vec will make operations like finding the last element in a chain much faster.

[Copilot]

Pull request overview

This PR refactors the Chain filter operation from a binary tree structure Chain(Filter, Filter) to a vector-based structure Chain(Vec<Filter>). The motivation is to improve performance during filter optimization, specifically making operations like finding the last element in a chain much faster.

Key Changes:

• Changed Op::Chain from storing two Filter arguments to storing a Vec<Filter>
• Updated all filter optimization algorithms (simplify, flatten, step, invert) to work with vector-based chains
• Modified parsing to accumulate chain elements into a vector
• Updated serialization/deserialization to handle variable-length chains
• Adjusted all filter application logic to iterate through chain vectors

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
josh-core/src/filter/op.rs	Changed Chain enum variant from two Filter parameters to Vec
josh-core/src/flang/parse.rs	Updated parsing to build chains as vectors, handling accumulation of multiple filters
josh-core/src/filter/persist.rs	Modified serialization to store variable-length chains; deserialization now reads arbitrary number of chain elements
josh-core/src/filter/opt.rs	Completely rewrote chain optimization logic to handle vectors: flattening nested chains, combining adjacent operations, and handling empty/single-element cases
josh-core/src/filter/mod.rs	Updated all chain-related operations (apply, unapply, lazy_refs, resolve_refs, path calculations) to iterate through vectors
josh-core/src/flang/mod.rs	Modified pretty-printing and spec generation to handle vector-based chains with special cases for empty and two-element chains
josh-core/src/build.rs	Updated chain builder function to wrap arguments in a vector
tests//.t	Test expectations updated to reflect new chain representation with flat numbering (chain/0, chain/1, chain/2) instead of nested (chain/0/chain/0/chain/0)

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[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

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