add_label bypasses kicad-sch-api serializer entirely — generates
s-expression strings and inserts them directly into the .kicad_sch
file via atomic write. Fixes two upstream bugs: global labels silently
dropped on save (serializer never iterates "global_label" key), and
local labels raising TypeError (parameter signature mismatch in
LabelCollection.add()).
add_power_symbol now falls back to sexp pin parsing when the API
returns None for custom library symbols (e.g. SMF5.0CA). Extracts
shared resolve_pin_position() utility used by both add_power_symbol
and batch operations.
Batch labels also fixed — collected as sexp strings during the batch
loop and inserted after sch.save() so the serializer can't overwrite
them.
kicad-sch-api has two parsing gaps: get_symbol_definition() returns
None for non-standard library prefixes (e.g. Espressif:ESP32-P4),
and there is no sch.global_labels attribute for (global_label ...)
nodes. This adds a focused parser that reads directly from the raw
.kicad_sch file as a fallback, integrated into the connectivity
engine, pin extraction, and label counting tools.
