fix: validate txpool transactions against next block height (#3172)

## Linked Issues/PRs
Closes #3169

## Description
When the TxPool validates transactions, it should use the next block
height (`current_height + 1`) rather than the current block height. This
is because transactions submitted to the pool will be executed in the
next block, not the current one.

This fix is particularly important for transaction expiration
validation. Previously, a transaction with an expiration height equal to
the current block height would be incorrectly accepted, only to fail
when actually executed in the next block (where it would already be
expired).

## Checklist
- [ ] Breaking changes are clearly marked as such in the PR description
and changelog
- [ ] New behavior is reflected in tests
- [ ] [The specification](https://github.com/FuelLabs/fuel-specs/)
matches the implemented behavior (link update PR if changes are needed)

### Before requesting review
- [x] I have reviewed the code myself
- [x] I have created follow-up issues caused by this PR and linked them
here

### After merging, notify other teams

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Co-authored-by: green <xgreenx9999@gmail.com>