[boyfeiyu]

Repeated contributions of the same @singleton class currently create separate objects within multibound lists and dictionaries. Respect the class decorator by sharing a class-specific cache key within each collection, and apply the scope to dictionary values before wrapping them with their keys.

Explicit binding scopes keep their existing per-contribution behavior, including scope=singleton and scope=noscope. Ordinary bindings, other provider kinds, and custom scopes retain their existing behavior.

Fixes #298. The regression test comes from @davidparsson's open draft #292, which currently contains the test without a production fix. This change does not implement the parent/child collection extension proposed in #324.

Validation on CPython 3.12.14 / macOS arm64:

• Full suite: 152 passed, 97.19% coverage.
• The original list regression and a separate replay of its dictionary assertion fail on current master and pass with this change.
• 25 additional independent checks passed, including construction counts, repeated/concurrent lookups, explicit scopes, dictionary keys, and injector isolation.
• mypy 1.7.1, Black 26.10.1, and check-manifest --no-build-isolation passed, using the repository's declared tool versions.

The other Python/PyPy and Linux CI environments have not been run locally.