Feat/sdk readonly client

[imotai]

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PR-Codex overview

This PR focuses on adding functionality and improving documentation for the db3.js library.

Detailed summary

• Added DatabaseStatePersistence message to db3_database_v2.proto
• Updated EventTable message in db3_database_v2.proto
• Updated query.test.ts by changing the timeout from 1000ms to 2000ms
• Updated types.ts by adding ReadClient to Client import
• Updated README.md with additional documentation and links
• Updated db_store_v2.rs by adding STATE_CF constant and implementing flush_state method
• Updated db_store_v2.rs by adding CollectionState and DatabaseState structs
• Updated db_store_v2.rs by updating the update_db_state_for_add_db method
• Updated database_v2.ts by updating the getCollection, getDatabase, and showDatabase methods
• Updated README.md with additional documentation and examples

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[codecov-commenter]

Codecov Report

Merging #536 (13be2b5) into main (1c8bce3) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

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@@            Coverage Diff             @@
##             main     #536      +/-   ##
==========================================
- Coverage   55.39%   55.38%   -0.01%     
==========================================
  Files          72       72              
  Lines       13994    13998       +4     
  Branches       61       61              
==========================================
+ Hits         7752     7753       +1     
- Misses       6242     6245       +3     

Flag	Coverage Δ
rust	55.38% <50.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/storage/src/db_store_v2.rs	60.20% <25.00%> (-0.21%)	⬇️
sdk/src/store/database_v2.ts	81.42% <100.00%> (ø)

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