runtime(js): fix useTemplate

[smorimoto]

Template is another one that is already widely used and documented.

[Copilot]

PR Overview

This PR updates various JavaScript runtime files to use template literals for string concatenation, thereby improving code readability and consistency.

• Updated string concatenation in file path calculations of fs_fake.js
• Replaced concatenated error messages and string operations with template literals in multiple runtime files
• Standardized formatting across modules including sys.js, fs.js, str.js, wasm/runtime.js, graphics.js, ieee_754.js, parsing.js, unix.js, ints.js, io.js, jslib.js, and marshal.js

Reviewed Changes

File	Description
runtime/js/fs_fake.js	Converted concatenation syntax in path and regex generation to template literals
runtime/js/sys.js	Updated error message and value formatting to template literals
runtime/js/fs.js	Standardized string concatenation for error messages and function returns
runtime/js/str.js	Reformatted escape sequence concatenation to use template literal
runtime/wasm/runtime.js	Changed string construction to template literals for clarity
runtime/js/graphics.js	Converted string concatenations for canvas operations into template literals
runtime/js/ieee_754.js	Updated float formatting functions to use template literals
runtime/js/parsing.js	Refactored log message concatenations to template literals
runtime/js/unix.js	Updated system error message construction to template literals
runtime/js/ints.js	Simplified integer conversion using String()
runtime/js/io.js	Converted error message concatenations to template literals
runtime/js/jslib.js	Updated log message formatting with template literals
runtime/js/marshal.js	Replaced string concatenation with template literals in error handling

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

[hhugo]

I don't like complex expressions inside templates. They makes review harder in my experience.
I think I would prefer if templates only embed simple identifiers.