Add aggregated gas metrics

We would like to propose to add to the PDP explorer a tab for showing some gas metrics.
The idea is to do something similar to [this](https://dashboard.starboard.ventures/transactions-usage) table from Starboard (at least as starting point):

### Version 1 (aggregate metrics):
List all the externally exposed functions from teh PDP proof smart contract (`PDPverifier`), as for example: createProofset, deleteProofset, addRoots, scheduleRemovals, provePossesion and nextProvingPeriod.
For each function, display the following metrics:
- the number of messages sent in the last 48h (or possibly 7 days),
- the total gas used (both absolute values and percentages),
- the total base fee and overestimation burn

This will provide sufficient data to calculate average gas usage and costs for each function type over the selected timeframe.
However, because PDP configuration (proofset size and number of roots) is flexible, Version 1 alone cannot accurately estimate the gas cost per GiB or per root. Therefore, we suggest adding Version 2 and potentially Version 3, see below.

### Version 2 (metrics filtered by number of roots):
For specific functions (for example: `provePossesion`), classify the messages in buckets based on number of roots in the proofset. Then for each bucket collects the same metrics listed in v1.
With this info, then we can show the daily average cost per root for performing PDP proofs (`provePossession`).

Open question: Are there other functions for which we need detailed reporting at the version 2 granularity?

### Version 3 (metrics filtered by number of roots and proofsetsize): :
Same as v2 but classify using two parameters instead of one: proofset size and number of roots.
(Comment: if this is not too complicate to visualize, maybe skip v2 and go directly with v3)
Take ranges for the number of roots value and for each range show the daily average cost per GiB.

cc @lucaniz

Start by reviewing the PDP explorer and the linked Starboard transactions-usage table, then inspect how externally exposed PDPverifier functions and message data are represented. Define the scope between aggregate metrics and filtering by roots or proofset size before implementation. Done means the explorer has a usable gas-metrics tab with agreed timeframe, function coverage, and gas, fee, and burn metrics.

Written by the indexing model from the issue text.