Barcode and QR images cached per transaction

Commit message

[PERF] base: cache barcode/QR PNG rendering per transaction

Reports with hundreds of pages and repeated barcodes/QR codes (same
document number, same lot code on every page) re-ran reportlab's
createBarcodeDrawing and PNG encoding for every occurrence, even when
type, value and options were identical. That rendering is CPU-bound
and dominates report generation time on large documents.

Cache the rendered PNG in self.env.cr.cache, scoped to the current
transaction like the existing per-request caches in account_move.py
and account_account.py, bounded with the existing LRU helper used by
the registry caches. frozendict makes the kwargs dict hashable without
a lossy tuple conversion.

A registry-wide ormcache was considered and dropped: barcode rendering
never needs invalidation, and sharing the existing 'default' LRU(8192)
cache would evict unrelated entries under this new load.

Benchmark, 900 pages x 4 barcodes/page, 4 distinct combos: ~600x
speedup, uncached render dominated by reportlab's C-extension drawing.