core/txpool: add some txpool metrics

[c98tristan]

This pull request includes several changes to replace the use of counters with meters for transaction metrics in the lending pool, order pool, and transaction pool. The most important changes include modifying various methods to use meters instead of counters and updating the metric definitions.

Metrics Update:

• core/tx_pool.go: Replaced counters with meters for various transaction metrics, including pendingDiscardMeter, pendingReplaceMeter, queuedDiscardMeter, and invalidTxMeter. Added new gauges for pendingGauge, queuedGauge, and localGauge. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

# TYPE txpool_invalid gauge
txpool_invalid 19

# TYPE txpool_local gauge
txpool_local 0

# TYPE txpool_pending gauge
txpool_pending 6

# TYPE txpool_pending_discard gauge
txpool_pending_discard 0

# TYPE txpool_pending_nofunds gauge
txpool_pending_nofunds 0

# TYPE txpool_pending_ratelimit gauge
txpool_pending_ratelimit 0

# TYPE txpool_pending_replace gauge
txpool_pending_replace 0

# TYPE txpool_queued gauge
txpool_queued 0

# TYPE txpool_queued_discard gauge
txpool_queued_discard 0

# TYPE txpool_queued_nofunds gauge
txpool_queued_nofunds 0

# TYPE txpool_queued_ratelimit gauge
txpool_queued_ratelimit 0

# TYPE txpool_queued_replace gauge
txpool_queued_replace 0

# TYPE txpool_underpriced gauge
txpool_underpriced 0

# TYPE txpool_valid gauge
txpool_valid 7763

• core/lending_pool.go: Updated methods to use meters instead of counters for tracking invalid, pending, and queued transactions. [1] [2] [3] [4] [5] [6] [7]

• core/order_pool.go: Modified methods to replace counters with meters for invalid, pending, and queued transactions. [1] [2] [3] [4] [5] [6] [7]

Reference:

• core, ethdb, metrics, p2p: expose various counter metrics for grafana ethereum/go-ethereum#19692
• core, metrics, p2p: switch some invalid counters to gauges ethereum/go-ethereum#20047
• core: dedup known transactions without global lock, track metrics ethereum/go-ethereum#20081