v0.7.2

Added

• samd gets a real build_samd() driver — the easiest of [0053]'s
  remaining nine driverless usermod ports to pick up next (esp8266 ruled
  out for tags too old to be worth it), modeled on rp2's own plain-Make
  shape rather than esp32/rp2's cmake one. No new provisioning step needed:
  like rp2, orchestrate.build() already generalizes sources. fetch_micropython() for it. Live-verified against real identifiers
  spanning v1.20.0 through the current tag; KNOWN_PORTS now carries
  seven wired drivers, not six. [0100].

Fixed

• rp2 and esp32 both passed tag_cflags()'s candidate CFLAGS_EXTRA
  straight into their build command with no probing, unlike every other
  cross-compiling port here — -Wno-error=unterminated-string-initialization
  (a gcc-15-only diagnostic, flagged for every tag v1.12-v1.25.0
  regardless of which toolchain a given row actually resolves to) hard-failed
  cc1: error: ... no option '-Wunterminated-string-initialization' on every
  pre-v1.26.0 row of either port, since both resolve to a sub-gcc-15
  toolchain there. Live-reproduced on v1.24.0-rp2-ADAFRUIT_FEATHER_RP2040
  (now producing a genuine firmware.uf2) and against a real ESP-IDF
  xtensa-esp-elf-gcc 14.2.0. Fixed the same way unix already was
  ([0082]): fetch/discover the real compiler first, then probe it with
  build_common.probe_supported_cflags() before building CFLAGS_EXTRA.
  esp32 has no static <prefix>gcc to point at, so its own fix discovers
  the real cross-compiler dynamically (a $PATH glob for *-elf-gcc, run
  after ESP-IDF's own install+export sequence) rather than guessing an
  idf_target -> prefix table. Neither bug had ever been exercised by CI --
  no workflow in this repo has built rp2/esp32 below v1.26.0. [0060].