SourceMap integration prep

[hrgdavor]

Fixes: #152

The addons are needed to support SourceMaps do not change WASM part. The remapping can be done outside the library but needs few small fixes to be implemented in non-hacky way.

Engine

One thing is that engine adds preamble of built-ins, and those have newlines that is not possible to discern without probing by running a small script that throws and inspecting it. That is not science fiction to do, but is engine can provide this info makes integration straight forward to do.

Since stderr and stdout getters are named like that, this code follows the convention.

Engine gets a field: preambleLineCount and getter preambleLineCount() that integration can use to reduce reported line number by before going int the SourceMap.

I agree with one more addition suggested by LLM in the engine:

public void resetOutput() {
    stdout.reset();
    stderr.reset();
}

It is generally useful for users to be able to reset these before reuse of the engine, and simplifies my sample integration I am using to test for my usage of quickjs4j down the line.

Runner

Runner just forwards preambleLineCount() and resetOutput().

Tests

Tests are LLM generated during the prototyping, they look ok.

Conclusion

During this impl I have thought few times about the SourceMap integration and concluded that it is better to be op-in as sourcemap is json so we do not force user into specific JSON lib.