Warn only for source-like suffix drops, batch ar argv, name non-iterable dependencies

The unmapped-suffix warning fired for every header-only library (the
default +<*> filter matches headers), so ArduinoJson would have warned
on every ESP8266 build. It now names exactly the source-like files
(.CPP, .ino and case-variants of the map) the case-sensitive suffix map
rejects, partial drops included, and stays quiet for headers and
metadata.

The ar shim batches the expanded object list by argv length (rc then q
appends), keeping the command line under the Windows 32767-char limit
the rspfile existed to avoid. A non-iterable dependencies value in a
manifest now warns by library name instead of raising a bare
TypeError.

tests/unit_tests/test_platformio_library.py

@@ -645,6 +645,9 @@ def test_normalize_dependencies_forms(caplog) -> None:
         {"name": "SPI"},
     ]
     assert normalize_dependencies("Wire") == [{"name": "Wire"}]
+    # A non-iterable value fails by manifest name, never a bare TypeError
+    assert normalize_dependencies(5, "libx") == []
+    assert "Ignoring unrecognized dependencies 5 of libx" in caplog.text
     # The dict-shorthand form validates names like the list form: an empty
     # key and a spec overriding name with a non-string both warn and drop
     assert normalize_dependencies(