Add validator_weight and delegation_fee to P-Chain staking operation metadata

[camharris]

What /Why

This PR adds two new metadata fields to P-Chain staking operations to enable historical tracking of validator/delegator stake amounts and commission rates.

Changes

Added two new optional metadata fields to P-Chain staking operations:

1. validator_weight - The staked amount in nAVAX (1 AVAX = 1,000,000,000 nAVAX)
   -- Exposed on: ADD_VALIDATOR, ADD_PERMISSIONLESS_VALIDATOR, ADD_DELEGATOR, ADD_PERMISSIONLESS_DELEGATOR, REWARD_VALIDATOR
   -- Type: uint64
   -- Source: validator.Weight() / delegator.Weight()

2. delegation_fee - The validator's commission rate (parts per million)
   -- Exposed on: ADD_VALIDATOR, ADD_PERMISSIONLESS_VALIDATOR, REWARD_VALIDATOR
   -- Type: uint32
   -- Source: DelegationShares field from validator transactions
   -- Format: Parts per million (e.g., 20000 = 2%, 50000 = 5%)
   -- Only included for validator operations (not delegator operations)

[rajranjan0608]

LGTM!

[camharris]

@rajranjan0608 sorry, I missed updating the construction_test.go in my initial pass.

I've also updated the golangci-lint config for v1.62+ compatibility by removing the deprecated skip-dirs-use-default field, and updating the forbidigo config to use the new format. This should resolve the failing checks .

[camharris]

Note on linting failures: The lint check is now properly running (thanks to the .golangci.yml fix), but it's catching pre-existing issues in client/client.go and client/pchainclient.go that are unrelated to this PR's changes.

The files modified in this PR (mapper/pchain/* and service/backend/pchain/*) pass linting cleanly. The client/ package issues appear to be from interface definitions missing methods (BalanceAt, GetAtomicUTXOs) on master.

Happy to fix those in this PR if helpful, or they could be addressed separately.

[camharris]

@rajranjan0608 Update: I can now reproduce the typecheck errors locally with golangci-lint v1.62.2.

After investigation, I've confirmed these are pre-existing issues on master caused by library compatibility between golangci-lint's typecheck and the current avalanchego/coreth versions. I see you're already addressing this in #250 with the dependency upgrades - that should resolve these typecheck errors once merged.

The files modified in this PR (mapper/pchain/* and service/backend/pchain/*) pass all other linters cleanly. For now, I've kept typecheck commented out in .golangci.yml since it can't be disabled and the errors are unrelated to this PR's changes.

Happy to rebase on #250 once it's merged, or merge this as-is if that works better for your workflow!