fix: formatter roundtrip for group qualifications, intervals, and expressions (#300)

[ronaldtse]

Summary

Fixes #300 — expressir format now produces output that can be re-parsed and produces the same model (structural content is stable across format iterations).

Root Cause

The formatter was outputting NOT {interval} which is ambiguous in EXPRESS — the parser sees NOT followed by { and cannot match it as an interval expression. The original code wraps intervals in parens: NOT ({interval}).

Changes

Formatter fixes

• Interval + unary expression: Wrap interval operands in parens when inside NOT
• Binary expression precedence: Use >= for same-precedence parenthesization
• AGGREGATE OF: Format with OF type when base_type is present
• Empty SELECT: Handle SELECT types with no items
• Binary literals: Value already includes % prefix

Builder fixes

• Shorthand variables: Fix double-wrapping of variable_id keys
• Procedure parameters: Same fix for formal parameters and procedure head parameters
• CASE statements: Proper case label and otherwise_statement handling
• AGGREGATE OF: Add builder support
• Type builder: Replace hash+define_method with explicit methods to fix autoload ordering
• Registry: Remove all send calls, remove duplicate registrations

Model fixes

• Remove HasWhereRules from Function/Procedure (EXPRESS spec compliance)
• Harden remark_attacher to use safe_get_collection for where_rules

Tests

• Add formatter_roundtrip_spec.rb with 10 test cases covering all fixed bugs
• Regenerate YAML and .exp fixtures to match improved builder output

Verification

• syntax.exp: roundtrips with structural content identical
• mathematical_functions_schema.exp (15K+ lines): roundtrips with structural content identical
• 103 specs pass, 0 failures
• Rubocop clean on all changed files