test: add unit tests for compare, math, case, condition, and repeat helpers

[Jitmisra]

PR Description:

Summary

Adds 52 dedicated unit tests for all 5 Handlebars helpers that previously had zero isolated test coverage. This directly addresses #80.

Tests Added

Helper	Tests	What's Covered
compare	12	All 8 operators (==, ===, !=, !==, <, <=, >, >=), all 16 named aliases (eq, equals, seq, strictly-equals, ne, not-equals, sne, strictly-not-equals, lt, less-than, lte, less-than-equals, gt, greater-than, gte, greater-than-equals), type coercion behavior, string lexicographic comparison, null/undefined handling, invalid operator error
condition	10	&&/and, ||/or, !/not operators with aliases, truthy/falsy coercion (0, "", null), combined usage with compare helper, invalid operator error
math	14	All 6 operators (+, -, *, /, **, %), modulo-by-zero error, division-by-zero → Infinity, floating point, negative numbers, string-to-number parsing, non-numeric input error, nested math operations, invalid operator error
case	7	upper/lower conversion, mixed case inputs, empty strings, numeric inputs, invalid type error
repeat	9	Basic repetition, repeat_index variable, 1-based indexing with math, zero count, negative count, single repeat, dynamic count, non-numeric error, context variable preservation

Approach

• Tests register helpers via HelperFactory.registerHelpers() in beforeAll
• Each test compiles a Handlebars template string and asserts the rendered output
• Error cases use expect().toThrow() to validate proper error messages
• Edge cases cover truthy/falsy coercion, type coercion, null/undefined, string comparison, and combined nested helpers

Results

• Before: 46 tests across 4 test suites
• After: 98 tests across 5 test suites (52 new tests, 0 failures)

File Changed

• tests/helpers/helpers.spec.ts — new file (342 lines)

[alondmnt]

Thank you @Jitmisra! I'll just replace single quotes with double quotes for eslint and merge this.