miner: optimize clear up logic for envs

[buddh0]

Description

miner: optimize clear up logic for envs

Rationale

1. Fix for bid.discard Conflict with worker.commit() Causing Panic

In bid_simulator.go, the bid.discard function conflicts with worker.commit(), resulting in a panic.
Specifically:

• At line 304, s.db.prefetcher is not nil.
• But at line 305, it suddenly becomes nil, causing a panic.

This happens due to concurrent modification of s.db.prefetcher.

Based on code analysis, this issue only occurs when a miner selects a bid as the final work to commit. There are two scenarios where this can happen after the worker calls GetBestBid:

• (a) bidSimulator.SetBestBid is invoked, or
• (b) a new chainHead event is received, triggering clearFn in bidSimulator.clearLoop.

This PR resolves the issue by delaying the discard action to avoid the race condition.

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2. Centralized Discard Logic in bidSimulator

Previously, environment discards (envs) were scattered across multiple locations within bidSimulator.

In this PR, we consolidate the logic so that environment discards happen in only one place, improving maintainability and reducing complexity.

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3. Optimizing clearLoop Iteration

In clearLoop, both bestBidToRun and simulatingBid retain up to b.chain.TriesInMemory() items.
Iterating over all of them is inefficient.

This PR introduces the use of GetFinalizedNumber to limit the retained items to just 2, significantly improving performance.

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Example

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Changes

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