feat : field completions

[Sypher845]

This PR adds field completion support to JETLS. When a user types x. and triggers completions (e.g., via Ctrl+Space), the server now suggests available fields for the inferred type of x.

[aviatesk]

This PR implements .-completion as "field completion", but in Julia, x.y is actually not a field access but it's a property access. That means x.-completion needs to be implemented in a way that emulates the behavior of getproperty(::typeof(x), ::Symbol). The current implementation calls fieldnames on the inferred type, which is the most reliable but incomplete way to statically emulate getproperty. Do you have any ideas on this?

Also, there should be additional points to discuss:

• ASTTypeAnnotator probably expects a complete AST in most cases. However, code like xxx.| might produce an incomplete AST. I'd like you to investigate what happens in which cases, and check whether the current approach still works fine.
• Please improve the completion trigger logic so that .| automatically triggers completion.

Lastly, please rebase this PR and set #620 as the merge target.

[Sypher845]

@aviatesk i have addressed the main review points,

• . now triggers completion automatically.
• dot completion now handles properties, not only fields.
• typed local dot completion still works, including incomplete cases like p. .
• displayed type details are postprocessed before showing them.

Current limitation:
for inferred non-constant values, custom property completion currently works for simple static propertynames(::T) cases, but not for all dynamic getproperty cases.

Please take a look when you have time

[codecov]

Codecov Report

❌ Patch coverage is 72.81553% with 84 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.23%. Comparing base (16ca32f) to head (3fc3361).
⚠️ Report is 28 commits behind head on avi/ASTTypeAnnotator.

Files with missing lines	Patch %	Lines
src/completions.jl	64.88%	46 Missing ⚠️
src/analysis/ASTTypeAnnotator.jl	84.10%	24 Missing ⚠️
src/utils/inference.jl	45.45%	12 Missing ⚠️
src/utils/binding.jl	60.00%	2 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           avi/ASTTypeAnnotator     #615      +/-   ##
========================================================
+ Coverage                 69.14%   69.23%   +0.09%     
========================================================
  Files                        51       53       +2     
  Lines                      8734     9034     +300     
========================================================
+ Hits                       6039     6255     +216     
- Misses                     2695     2779      +84     

Flag	Coverage Δ
JETLS.jl	69.23% <72.81%> (+0.09%)	⬆️

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