fix: add SourceMapConsumer cleanup, handle unmapped and bare stack lines

[Tejakshaya]

• Call smc.destroy() after use to free WASM memory allocated by source-map
• Show unmapped positions instead of silently dropping stack lines with no source map entry
• Handle file:line:col stack lines that have no method name (e.g from react native traces)
• Remove leftover dev comment

What was wrong and why:

1. Missing smc.destroy() <- WASM memory leak
   source-map's SourceMapConsumer allocates WASM memory that must be explicitly freed via destroy(), the call was missing entirely

2. Silent line drops when source map has no mapping
   When smc.originalPositionFor() returns { line: null } the code produced zero output for that stack frame, users see gaps in their translated trace with no indication a line was present but unmapped. Now falls back to printing: atmethodName (line N:col)

3. Bare file:line:col lines parsed with leading whitespace in filename
   Stack traces from React Native include lines like:

   main.jsbundle:954:5353

(no method name, trailing space). The existing regex only matched file:line:col method, these bare lines fell through to stacktrace-parser which included leading whitespace in the filename which ended up causing originalPositionFor to silently fail so added a second regex to reformat these as at <unknown> (file:line:col)