fix: escape single quotes and backslashes in IR string output

[AugustHagedal]

Summary

• Strings containing ' or \ in their value broke the IR parser because appendQuotedString emitted them unescaped inside single-quote delimiters (a TODO comment had flagged this since the file was written)
• The LiteralString IR case had its own inline template that bypassed appendQuotedString entirely, so it also emitted unescaped strings

Changes

• Add escapeIRString() helper in IRtoString.ts that escapes \, ', \n, \r, and \t
• Apply it in appendQuotedString(), removing the long-standing TODO(simon): Escape quotes comment
• Fix the LiteralString case to route through appendQuotedString instead of its own inline template literal
• Add two regression tests: single quote and backslash in string literals (120 tests, all passing)

Test plan

• Run existing test suite — all 118 tests continue to pass
• New test: escapes single quotes in string literals — verifies storestring 'it\'s a test'
• New test: escapes backslashes in string literals — verifies storestring 'C:\\Users\\file'

Tests: 120 passed, 120 total

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