Arithmetic expression support

[colemancda]

Implements ArithmeticExpression (CoreModel 2.11.0) as native SQL, replacing the previous invalidPredicate rejection.

Translation

(a <op> b) <operator> constant compiles to a parenthesized SQL expression with positional bindings, recursively for nested operands. SQLite's native operators match CoreModel's in-memory engine where it matters:

• / truncates when both operands are INTEGER (7 / 2 is 3) and promotes to REAL when either is floating point
• division or remainder by zero yields SQL NULL, which fails every comparison — the same observable outcome as the engine's nil

Deliberate divergence handling

• .modulus with a statically-known non-integer operand is rejected (invalidPredicate) rather than translated: SQLite's % casts operands to INTEGER, but CoreModel defines remainder for integers only, and a silently cast result would differ between backends. Operand types are resolved from the entity description (composite element columns included); unknown types (e.g. a custom function's result) pass through, where NULL propagation makes a wrong guess harmless.
• The only knowing divergence is at the edges of Int64: the in-memory engine wraps, SQLite promotes an overflowing INTEGER result to a REAL approximation. Documented in the source.

Testing

10 new tests against real SQLite files: integer add/divide/modulus, truncation, division-by-zero across three operators, float promotion, float-modulus rejection, nested expressions, compound predicates — plus a sweep asserting SQL and in-memory evaluation return identical row sets for the same inputs. All 127 tests pass.

[github-code-quality]

Code Coverage Overview

Languages: Swift

Swift / code-coverage/llvm-cov

The overall coverage in commit 26e78be in the feature/arithmetic-e... branch is 98%. The coverage in commit 1cdf583 in the master branch is 99%.

Show a code coverage summary of the most impacted files.

File	master 1cdf583	feature/arithmetic-e... 26e78be	+/-
Sources/CoreMod...Predicate.swift	99%	96%	-3%