fix: batch fix ~40 bugs across codebase

Template fix (affects all 1032 generated methods):
- Fix callErr variable shadowing: `:=` in closure created new variable
  that shadowed outer callErr, silently losing JNI errors
- Capture vm.Do() return value: thread attach errors were discarded
- Both fixes together ensure all JNI errors propagate to callers

Code generator fixes:
- Handle bare "CharSequence" as string type in ResolveType
- Handle CharSequence in mergeParam and mergeCallback isString checks
- Remove redundant nil check in Field.GetterName()
- Remove redundant MergedMethod.Error field (HasError suffices)

Core JNI fixes:
- NewString: guard against empty unicodeChars slice panic
- DefineClass: guard against empty class bytes panic
- GetStringRegion/GetStringUTFRegion: guard against empty buf panic

Example resource leak fixes:
- accounts: free GlobalRef per account element after use
- lights: free GlobalRef per Light and LightState after use
- session: free GlobalRef per MediaController after use
- print: free GlobalRef for Job and JobInfo after use
- usb: remove redundant NewGlobalRef wrapping, free refs after use
- power: add missing defer mgr.Close()
- ir: remove crash-causing nil pattern Transmit call
- location: fix comment saying 15s when code uses 30s

Regenerated all packages with template fix applied.

Author: xaionaro@dx.center