refactor: organise LSP backed + improved diagnostics

[KyrylR]

Refactors the LSP analysis pipeline while fixing semantic highlighting and cross-file diagnostics.

Semantic highlighting

• Replaces string-length-based call highlighting with lexer/span-based token extraction.
• Highlights only callable identifiers instead of entire generic call expressions.
• Separately highlights built-ins and function-valued generic arguments, such as array_fold and consume_budget.
• Leaves punctuation, numeric bounds, and generic syntax to TextMate.
• Preserves jet namespace/function splitting, macros, type casts, declarations, and UTF-16-safe positions.

Cross-file diagnostics

• Retains compiler source maps in each analysis result.
• Publishes imported-file errors against their actual file URI and source range, including unopened files.
• Supports code, file-wide, and global diagnostic locations.
• Preserves secondary labels as related information and includes compiler notes/help.
• Retains filtering for synthetic entry-point noise and remapping for duplicate imported main errors.

Architecture

• Introduces AnalysisSnapshot as the immutable result of analyzing an open root.
• Introduces SourceSet as the authoritative compiler file-ID-to-URI/text mapping.
• Extracts semantic tokens, diagnostics, and navigation into dedicated modules.
• Introduces WorkspaceState to own open-root analyses and diagnostic publication policy.
• Moves parsing, dependency resolution, type checking, source-map preservation, and visible-function construction out of the LSP backend.
• Reduces the backend to protocol handling and feature orchestration.
• Simplifies general utilities by moving analysis-specific logic into appropriate modules.

Diagnostic lifecycle

• Atomically replaces each root’s diagnostic contribution.
• Clears stale diagnostics when dependencies disappear or errors are corrected.
• Aggregates and deduplicates diagnostics from roots sharing a dependency.
• Gives directly analyzed unsaved buffers precedence over saved dependency copies.
• Recomputes diagnostics when documents close.
• Rejects stale analysis results by document version.
• Sends versions only for directly analyzed documents.

Validation

• Adds regression coverage for generic calls, built-ins, casts, jets, macros, UTF-16 positions, imported-file ranges, unopened dependencies, shared dependencies, deduplication, unsaved-buffer precedence, stale cleanup, document close, and duplicate imported main.
• Rust tests, strict Clippy, formatting checks, and the complete VS Code validation suite pass.

[gerau]

ACK 66d21d5; tested locally with VScode

comments are small nits, otherwise it is looking good