Fix mlx-swift-lm dependency to use semantic versioning

[alexey1312]

Summary

• Replace branch: "main" with from: "2.29.3" for mlx-swift-lm dependency

Problem

When consumers try to use AnyLanguageModel with semantic versioning:

.package(url: "...", from: "0.5.3")

SPM fails to resolve dependencies because branch: "main" is incompatible with version-based transitive dependency resolution:

error: exhausted attempts to resolve the dependencies graph, with the following dependencies unresolved:
* 'mlx-swift-lm' from https://github.com/ml-explore/mlx-swift-lm

Solution

Pin mlx-swift-lm to version 2.29.3 (latest stable release) instead of tracking the main branch.

Test plan

• swift package resolve succeeds
• swift build succeeds

[mattt]

@alexey1312 Thank you for this PR. I believe the guidance from mlx-swift-lm to pin to a semantic tag is relatively new. Or at least is new since they migrated from mlx-swift-examples. I'm just as happy to do it this way to allow for semantic versioning.

Taking a look at this now to see what the earliest version is that will work, to make the constraint as loose as possible (and therefore less likely to cause conflicts).

[mattt]

Alright, so apparently mlx-swift-lm introduced some ToolSpec/tool-call APIs and the UserInput.chat/tools initializer MLXLanguageModel uses in a patch release (2.25.4 → 2.25.5). So let's target that with a from:. If a package consumer pins to a later version or more strictly, like .upToNextMinor(from: "2.30.0"), this should resolve no problem.