Parallel read-only transaction execution further improvement

[linh2931]

During code walkthrough led by Kevin, the following improvements were suggested. They can be done during RC phases or later.

• Use deque instead of std::deque. PR [4.0 -> main] Small improvements for parallelizing read-only transactions and tasks #946
• Pick a value that seems somewhat reasonable for read and window time. Or put a comment indicating the default values are just numbers. No need to do in code. Should be in a document.
• Would be nice to encapsulate mutex in _ro_trx_queue by adding a push/pop to _ro_trx_queue. (moved to Read-only transaction processing - prevent thread starvation while in the read window. #822)
• Add comment that window timers only accessed from the main thread. PR [4.0 -> main] Small improvements for parallelizing read-only transactions and tasks #946
• Consider using only one timer since only one window should be active at any given time. PR [4.0] Use a single timer for read and write windows #905
• Pass in read_window_deadline so that it is calculated before these are spawning. #PR 901
• start_recover_keys may not needed. PR [4.0] Execute read only safe tasks on read-only thread pool #901
• EOS_ASSERT chain.is_building_block(). No longer applicable as we allow producer in test mode.
• calculate_block_deadline is not needed. No longer applicable as the code is refactored to handle read-only trxs in both main thread and read-only threads.
• Update cap on read-only threads when runninng with OC to reflect behavior described in document. PR [4.0 -> main] Small improvements for parallelizing read-only transactions and tasks #946