fix(diff): handle Symbol values in direct() without throwing

[terminalchai]

Problem

Comparing a Symbol to any other type (e.g. a number) via assert.is or assert.equal causes an uncaught TypeError instead of a readable diff failure:

TypeError: Cannot convert a Symbol value to a string
    at direct (uvu/diff/index.mjs:136:29)
    at compare (uvu/diff/index.mjs:218:9)
    at assert (uvu/assert/index.mjs:32:28)

The crash originates in direct() which calls input += ' '.repeat(...) + [${typeA}] — but JS throws when trying to coerce a Symbol via +=.

Fixes #251

Root cause

direct() only coerced with String() in the default parameter expressions (to compute the initial lengths), but kept the raw values afterward. The crash surfaced the moment code tried to do symbolValue += someString.

Fix

Capture typeof before coercing (so the type-mismatch display still shows [symbol] / [number] correctly), then immediately coerce both input and expect to strings via String():

 export function direct(input, expect, lenA = String(input).length, lenB = String(expect).length) {
+  // Capture original types before coercion so that type-mismatch display works.
+  let typeA=typeof input, typeB=typeof expect;
+  // Coerce to strings up-front so that Symbols (and other non-string primitives
+  // that throw on implicit + coercion) do not cause an uncaught TypeError.
+  input = String(input);
+  expect = String(expect);
   let gutter = 4;
   let lenC = Math.max(lenA, lenB);
-  let typeA=typeof input, typeB=typeof expect;

Changes

• src/diff.js - 4-line guard at the top of direct()
• test/diff.js - 2 new direct snapshot cases + 1 compare case for Symbol vs number

Verification

Manually verified against actual outputs (test infra uses legacy esm pkg incompatible with Node 22 - a pre-existing issue unrelated to this fix):

PASS: direct(Symbol('foo'), 42) does not throw
PASS: direct(42, Symbol('foo')) does not throw
PASS: compare(Symbol('foo'), 42) does not throw
PASS: direct(123, 456) still works
PASS: direct(123, '123') still shows type mismatch
5 passed, 0 failed