feat: define PendingTransactionStorage interface and TransactionPoolService interface

[natanasow]

Description

New interfaces for the new classes part of the TransactionPool feature will have to be created in order to ensure modularity and not relying on concrete implementations

Motivation

• Decouple transaction-pool logic from any specific cache implementation

• Allow operators to plug in Redis, in-memory LRU, SQL, or other stores

export interface TransactionPoolService {
  saveTransaction(address: string, tx: Transaction): Promise<void>;

  onConsensusResult(): Promise<void>;

  getPendingCount(address: string): Promise<number>;
  
  resetState(): Promise<void>;
}

export interface PendingTransactionStorage {
  getList(addr: string): Promise<number>;

  addToList(addr: string, expectedPending: number): Promise<{ ok: true; newValue: number } | { ok: false; current: number }>;

  removeFromList(address:string, transaction: string): Promise<number>;
  
  removeAll(): Promise<void>;
}

Related issue(s)

Fixes #4388

Testing Guide

Changes from original design (optional)

N/A

Additional work needed (optional)

N/A

Checklist

• I've assigned an assignee to this PR and related issue(s) (if applicable)
• I've assigned a label to this PR and related issue(s) (if applicable)
• I've assigned a milestone to this PR and related issue(s) (if applicable)
• I've updated documentation (code comments, README, etc. if applicable)
• I've done sufficient testing (unit, integration, etc.)

[github-actions]

Test Results

 20 files  ±0  265 suites  ±0   18m 49s ⏱️ -12s
726 tests ±0  721 ✅ ±0  5 💤 ±0  0 ❌ ±0 
742 runs  ±0  737 ✅ ±0  5 💤 ±0  0 ❌ ±0 

Results for commit a274b50. ± Comparison against base commit c5c5433.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 86 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/relay/src/lib/types/transactionPool.ts	0.00%	86 Missing ⚠️

❌ Your patch status has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

@@                    Coverage Diff                    @@
##           feat/transaction-pool    #4405      +/-   ##
=========================================================
- Coverage                  96.10%   95.69%   -0.42%     
=========================================================
  Files                        121      122       +1     
  Lines                      19940    20026      +86     
  Branches                    1755     1755              
=========================================================
  Hits                       19164    19164              
- Misses                       751      837      +86     
  Partials                      25       25              

Flag	Coverage Δ
config-service	98.80% <ø> (ø)
relay	90.28% <0.00%> (-0.49%)	⬇️
server	88.82% <ø> (ø)
ws-server	98.27% <ø> (ø)

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

Files with missing lines	Coverage Δ
packages/relay/src/lib/types/transactionPool.ts	0.00% <0.00%> (ø)

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