Add per-transaction gas limit to block building docs

[niran]

We're changing the transaction gas limit on Base next month. This PR adds documentation for that limit, plus a warning about the upcoming change that will be removed after it has been activated.

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[danyalprout]

Thanks for adding this, looks great overall. The main thing that stuck out is whether we should state this as a change to block building (I personally think so), right now it feels separate due to the layout. If so there are two changes I think we should make:

1. Move the section your added under the configurations
2. Add it as an upcoming deployment w/ a date to the overview table, e.g. `Flashblocks + Transaction Gas Limits (Xth Sept)

[cb-heimdall]

Review Error for danyalprout @ 2025-08-21 08:34:34 UTC
User failed mfa authentication, either user does not exist or public email is not set on your github profile. \ see go/mfa-help

[Alexcruz3333]

ok