size gate: emit flash_bytes from ELF for targets without a packaged .bin (#10940)

* size gate: emit flash_bytes from ELF for targets without a packaged .bin

nRF52 builds package hex/uf2/DFU zip but no raw .bin, so collect_sizes.py
dropped budgeted envs like rak4631 entirely and the size-budget-gate failed
closed. Emit ELF text+data as flash_bytes in the manifest and use it as the
fallback flash measurement.

* Factor shared size-tool invocation into run_size_tool helper

bin/collect_sizes.py

@@ -5,10 +5,13 @@
 Output schema (consumed by bin/size_report.py):
     {"<env>": {"flash_bytes": <int>, "ram_bytes": <int>}}
 
-flash_bytes is the size of the main firmware image (.bin). ram_bytes is the
-static RAM footprint (.data + .bss) emitted into the manifest by
-bin/platformio-custom.py; it is omitted for manifests that predate it, and
-size_report.py renders those as "n/a".
+flash_bytes is the size of the main firmware image (.bin); for targets whose
+packaged artifacts include no raw .bin (e.g. nRF52) it falls back to the
+flash_bytes value (ELF text + data) emitted into the manifest by
+bin/platformio-custom.py. ram_bytes is the static RAM footprint (.data + .bss)
+emitted into the manifest by bin/platformio-custom.py; either metric is
+omitted for manifests that predate it, and size_report.py renders those as
+"n/a".
 """
 
 import json
@@ -42,11 +45,19 @@ def collect_sizes(manifest_dir):
                 ):
                     bin_size = entry["bytes"]
                     break
+        # Fallback: flash footprint emitted into the manifest (ELF text + data),
+        # for targets that package no raw .bin (e.g. nRF52 hex/uf2/DFU zip)
+        if bin_size is None:
+            flash_bytes = data.get("flash_bytes")
+            if isinstance(flash_bytes, int) and not isinstance(flash_bytes, bool):
+                bin_size = flash_bytes
+        entry = {}
         if bin_size is not None:
-            entry = {"flash_bytes": bin_size}
-            ram_bytes = data.get("ram_bytes")
-            if isinstance(ram_bytes, int) and not isinstance(ram_bytes, bool):
-                entry["ram_bytes"] = ram_bytes
+            entry["flash_bytes"] = bin_size
+        ram_bytes = data.get("ram_bytes")
+        if isinstance(ram_bytes, int) and not isinstance(ram_bytes, bool):
+            entry["ram_bytes"] = ram_bytes
+        if entry:
             sizes[board] = entry
     return sizes