Keep per-file bars when sizes are unknown; harden the prefetch probes

An unknown Content-Length (probe failure, non-2xx, or a CDN omitting it
on HEAD) now skips the parallel prefetch so the sequential downloads
keep their per-file bars, instead of a silent multi-MB batch; the HEAD
helper returns None for unknown, distinct from a genuine zero, and
catches only RequestException. The cache probe logs its failure at
debug. The espidf tool prefetch reads sizes with .get so a missing size
only drops the bar instead of aborting the resumable prefetch. The
idedata warning logs its traceback at debug for parser regressions, and
framework_helpers joins the ESP-IDF infra CI triggers it is imported
by.

script/determine-jobs.py

@@ -535,6 +535,7 @@ ESP_IDF_INFRA_TRIGGER_PATH_PREFIXES = ("esphome/espidf/", "esphome/build_helpers
 ESP_IDF_INFRA_TRIGGER_FILES = frozenset(
     {
         "esphome/build_gen/espidf.py",
+        "esphome/framework_helpers.py",
         "esphome/platformio/library.py",
         "esphome/platformio/extra_script.py",
     }