feat(networks): source-pin base-anvil to the Cobalt precompile set (BOP-453)

[robriks]

Summary

The base-anvil half of the Cobalt fork-test snapshot pair (BOP-453, under BOP-428). Makes --base install the complete Cobalt precompile set so the base/base #4102 LIVE conformance suite (base-std #173) can run against a Cobalt-dispatching base-anvil.

Per the ratified snapshot strategy (BOP-427 → BOP-453/454), fork selection is source-pinned, not a runtime flag:

• Fork is a single compile-time constant BASE_PRECOMPILE_UPGRADE (this snapshot: Cobalt). The installer, trace labels, precompile map, and sentinel warming all key off it, so re-pinning to another fork (e.g. the Beryl pair) is a one-line change.
• Cobalt install mirrors the upgrade >= Cobalt arm of BasePrecompiles::install: the Beryl singletons plus the EIP-8130 TxContext + NonceManager, with the ActivationRegistry handed a state-backed admin config.
• No public runtime selector. The earlier --base-fork CLI flag / base_fork config key (and its parser, serde adapter, and CLI tests) are removed, matching BOP-453's explicit "do not add --hardfork/--base-fork" scope.

Relationship to earlier revision

This PR originally added a public --base-fork runtime selector. That approach was superseded by the commit-pair strategy from BOP-427; the latest commit reworks it to the source-pinned form above. (Happy to squash the two commits into one before review.)

Test plan

• cargo test -p foundry-evm-networks — green against the current pin (base/base 1090a1ba, revm 41): snapshot_pins_cobalt, base_installs_complete_cobalt_precompile_set, without_base_installs_nothing.
• cargo clippy and cargo fmt --check clean.
• LIVE: base/base #4102 conformance suite (base-std #173) against this snapshot at Cobalt.

Open question — merge target

Pinning Cobalt means merging this to base-anvil-fork would flip the shipped --base default from Beryl to Cobalt. If mainline must track the live fork (Beryl), this branch should be treated as the pinned Cobalt snapshot artifact (record its SHA for the base/base CI + BOP-453) rather than merged. Flagging for a call before this leaves draft.

[linear]

BOP-428

BOP-453

[stephancill]

I believe we opted to keep the head of base-anvil up to date with the latest upgrade and allow checking out older forks using git (tracked here https://github.com/base/base/blob/main/.github/workflows/base-std-fork-tests.yml#L33-L36)

[robriks]

Closing as redundant / superseded.

The team's direction is branch-per-fork, not a runtime --base-fork selector:

• base-anvil-fork (main) is already retargeted to Cobalt (c2dc6c4) on the updated base/base activation API (b467e06, pin dab0d0a2), so --base installs the complete Cobalt set there.
• release/v1.1.x stays Beryl (see fix(networks): thread BaseUpgrade through activation install (Beryl) #59).

The base-anvil Cobalt fork-test snapshot (BOP-453) is therefore a base-anvil-fork commit (current tip ae7557c), so this PR's compile-time BASE_PRECOMPILE_UPGRADE constant + earlier --base-fork runtime exploration is no longer needed. Branch is left in place for history.