Add DbSnapshot to sov-db-schema

[citizen-stig]

Description

This PR adds: DbSnapshot, a wrapper around sov_schema_db::DB, which has it's local cache in form of adapted SchemaBatch and link to QueryManager. This allows DbSnapshot read/write value to local cache, fetch them from parent snapshots or directly from DB.

Please note, that this functionality is added, but it is not integrated. Next step would be modifying StateDB, NativeDB and LedgerDB to work with DbSnapshot instead of DB directly.

Main modifications:

• *sov_schema_db::SchemaBatch: vector of operations replaced with HashMap, which allows efficient reads.
• internal Mutex is removed from SchemaBatch and now it is responsibility of the caller to handle. Current usage of SchemaBatch is not concurrent. DbSnapshot uses Mutex over whole internal cache. Potentially related to Make writes of SchemaBatches atomic across StateDb's JmtNodes, JmtValues, and NativeDb's accessory state #791

Linked Issues

• Related to Data Availability re-orgs handling tracking issue #1023

Testing

New integration test has been added to test snapshot

Docs

Documentation to the new modules have been added

[codecov]

Codecov Report

Merging #1112 (693724f) into nightly (8b4eb37) will increase coverage by 0.1%.
Report is 4 commits behind head on nightly.
The diff coverage is 93.5%.

Files	Coverage Δ
full-node/db/sov-db/src/native_db.rs	100.0% <100.0%> (ø)
full-node/db/sov-schema-db/src/lib.rs	92.7% <96.7%> (+4.1%)	⬆️
full-node/db/sov-schema-db/src/snapshot.rs	92.1% <92.1%> (ø)

... and 2 files with indirect coverage changes

[neysofu]

LGTM!