fix(core): prevent infinite recursion for recursive tuples (#5089)

[NathanKneT]

Fix recursive tuple infinite recursion regression (#5089)

Problem

Recursive tuples that worked in Zod v3 throw TypeError: Cannot read properties of undefined (reading '_zod') in v4 during schema initialization.

Root Cause

$ZodLazy and $ZodReadonly constructors access properties on potentially uninitialized schemas during circular reference scenarios.

Solution

• Add optional chaining (?.) for safe property access in lazy getters
• Minimal change preserving performance and architecture
• No breaking changes to existing functionality

Changes

• src/v4/core/schemas.ts: Add optional chaining to property access in $ZodLazy and $ZodReadonly constructors
• src/v4/core/tests/recursive-tuples.test.ts: Comprehensive regression test suite

Testing

• ✅ All existing tests pass
• ✅ New tests cover recursive tuple patterns from the issue
• ✅ Verifies both schema creation and parsing work correctly
• ✅ Maintains backward compatibility

Before/After

Before (broken):

const y = z.lazy((): any => z.tuple([y, y]).or(z.string()));
y.parse(["a", ["b", "c"]]); // TypeError: Cannot read properties of undefined