Split the 3655-line data_usage_define.rs (59% inline tests) into a
canonical foo.rs + foo/ module tree with zero behavior change:
- data_usage_define.rs (~950): cache constants and revision helpers,
the data-usage tree types, DataUsageCacheInfo with its hand-written
Serialize, the in-memory tree operations, dui, and marshal/unmarshal
- data_usage_define/persistence.rs (~580): the load/backup/restore
ladder (load, try_load_inner, revision_for_path) and the CAS save
path with its retry policy and save metrics
- data_usage_define/tests.rs (~2155): the inline test module as a child
module
All module paths are unchanged (the lib.rs data_usage_define::* glob
re-export and every crate::data_usage_define:: consumer resolve as
before). The hand-written map-encoded Serialize for
DataUsageCacheInfo is moved byte-for-byte per the AGENTS.md
cross-cutting invariant; on-disk names and the cache key format const
stay in the root. Four persistence helpers used by tests gain
pub(super), whose scope equals the old single-module privacy domain.
Code is moved verbatim apart from those markers, per-module import
headers, and rustfmt re-wraps.
Co-authored-by: heihutu <heihutu@gmail.com>
houseme