refactor(test-rpc): unify batch request chunking

[LouisTsai-Csie]

Description

There are two unrelated batch-size constants:

• In send_wait_transactions, EthRPC.DEFAULT_MAX_TRANSACTIONS_PER_BATCH is configured to 750. This restricts the number of transactions sent per iteration: send them, wait for them, and then do the next iteration.
• In get_transaction_receipts, the batch size is configured to 500 (chunk size). The same restriction could be applied to get_balances, get_codes, get_transactions_by_hash, send_transactions,get_account and get_alloc, none of which chunk today.

In this PR, I lift the transport chunking into post_batch_request and collapse both constants into a single BaseRPC.max_batch_size (default 750), so every batched method is chunk-safe. get_transaction_receipts drops its
own chunking loop, and send_wait_transactions keeps its loop but reads the shared limit.

The constructor argument and pytest fixture are renamed from max_transactions_per_batch to max_batch_size; the --max-tx-per-batch lag keeps its name.

Notable behavior change: --max-tx-per-batch now also caps receipts, balances, code and account state batches, and receipt batches grow from 500 to 750.

Related Issues or PRs

Follow up on PR #3298 , comment #3298 (review)

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards & Verifying Changes: just static
• PR title has the form <type>(<area>): <title>, where <type> and <area> come from an appropriate C-<type>, respectively A-<area>, label. The title should match the target squash commit message.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.50%. Comparing base (07424a8) to head (89d9917).
⚠️ Report is 5 commits behind head on forks/amsterdam.

Additional details and impacted files

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##           forks/amsterdam    #3327   +/-   ##
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  Coverage            93.50%   93.50%           
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  Files                  624      624           
  Lines                37070    37070           
  Branches              3394     3394           
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  Hits                 34661    34661           
  Misses                1653     1653           
  Partials               756      756           

Flag	Coverage Δ
unittests	93.50% <ø> (ø)

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[spencer-tb]

Small nit, otherwise LGTM!

[github-actions]

Successfully created backport PR for benchmarks/amsterdam:

• refactor(test-rpc): unify batch request chunking [backport benchmarks/amsterdam] #3331