config: use struct instead of Dict

[abap34]

Summary

This PR changes the configuration storage object from a Dict to a struct (JETLSConfig).
This enables:

• Better compiler understanding of configuration fields, improving LS performance
• Automatic schema generation for completion and validation

Implementation Details

A new dependency, Configurations.jl, has been introduced.
This package maps TOML-parsed Dicts to structs.
It’s relatively lightweight, so adding it as a dependency should not be a significant issue.

Since Configurations.jl does not currently provide full key paths for nested KeyErrors,
the helper function collect_unmatched_key from the previous implementation remains temporarily for error reporting.
I plan to submit a PR to Configurations.jl to support this feature, so that, this workaround can be removed.

Schema Generation

With JSONSchemaGenerator.jl,
a JSON Schema can be generated simply as follows:

StructTypes.omitempties(::Type{T}) where {T <: ConfigSection} = fieldnames(T)
JSON.json(JSONSchemaGenerator.schema(JETLSConfig), 4)

Using this approach, completion and type checking become available in various editors.
(The example below uses VSCode with even-better-toml.)

In the long term, it would be convenient to have the schema generated in CI at release time and registered to schemastore.org. This part is not critical for the LS itself, so we can be more liberal in using convenient tools and dependencies to improve the workflow.

I would be happy to discuss this further later on :)

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.88%. Comparing base (de2b185) to head (b7aa529).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/types.jl	62.50%	9 Missing ⚠️
src/formatting.jl	0.00%	4 Missing ⚠️
src/testrunner/testrunner.jl	0.00%	4 Missing ⚠️
src/config.jl	95.65%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #282      +/-   ##
==========================================
+ Coverage   70.53%   70.88%   +0.34%     
==========================================
  Files          38       38              
  Lines        3662     3647      -15     
==========================================
+ Hits         2583     2585       +2     
+ Misses       1079     1062      -17     

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[aviatesk]

Thanks so much for working on this, @abap34