refactor: harden codebase and remove unicode artifacts

- fix urllib.parse.quote import (was urllib.request.quote)
- add operator precedence parens in generate_pack dedup check
- narrow bare except to specific types in batocera target scraper
- cache load_platform_config and build_zip_contents_index results
- add selective algorithm support to compute_hashes
- atomic write for fetch_large_file (tmp + rename)
- add response size limit to base scraper fetch
- extract build_target_cores_cache to common.py (dedup verify/pack)
- hoist _build_supplemental_index out of per-platform loop
- migrate function-attribute caches to module-level dicts
- add @abstractmethod to BaseTargetScraper.fetch_targets
- remove backward-compat re-exports from common.py
- replace em-dashes and unicode arrows with ASCII equivalents
- remove decorative section dividers and obvious comments

scripts/truth.py

@@ -217,7 +217,7 @@ def generate_platform_truth(
             sys_cov["profiled"].add(emu_name)
 
     # Ensure all systems of resolved cores have entries (even with 0 files).
-    # This documents that the system is covered — the core was analyzed and
+    # This documents that the system is covered -the core was analyzed and
     # needs no external files for this system.
     for emu_name in cores_profiled:
         profile = profiles[emu_name]
@@ -261,9 +261,7 @@ def generate_platform_truth(
     }
 
 
-# -------------------------------------------------------------------
 # Platform truth diffing
-# -------------------------------------------------------------------
 
 def _diff_system(truth_sys: dict, scraped_sys: dict) -> dict:
     """Compare files between truth and scraped for a single system."""
@@ -430,7 +428,7 @@ def diff_platform_truth(truth: dict, scraped: dict) -> dict:
         else:
             summary["systems_fully_covered"] += 1
 
-    # Truth systems not matched by any scraped system — all files missing
+    # Truth systems not matched by any scraped system -all files missing
     for t_sid in sorted(truth_systems):
         if t_sid in matched_truth:
             continue