Add immutable_account_mutated dylint detector

[maxkup19]

Summary

• Implement immutable_account_mutated as a dylint detector (extension/detectors/immutable_account_mutated/) using LateLintPass HIR analysis
• Remove the built-in syn-based ImmutableAccountMutatedDetector from the language server registry (replaced by the dylint version)
• Add DiagnosticRelatedInformation support to the dylint diagnostic pipeline — detectors can now emit bidirectional navigation links (e.g., mutation site ↔ field declaration)
• Clean up dead code across the language server (unused loader, cache methods, compiler helpers, anchor pattern utilities)

Detection strategy

The lint checks public functions with Context<T> parameters, resolves the Accounts struct T, identifies fields of type Account/AccountInfo/AccountLoader without #[account(mut)] or #[account(init)], and walks the function body for mutations (assignments, compound assignments, &mut borrows, mutating method calls). Emits warnings on both the mutation site and the field declaration with clickable cross-references.