chore(Distributor): remove pre-Pectra permissionless distributeFor path

[sailorpepe]

Closes #25

What

Removes dead code from the pre-Pectra permissionless reward distribution path. The Pectra11 hard fork made distributeFor(uint64, uint64, bytes, bytes32[], bytes32[]) permanently unreachable — only the system-call distributeFor(bytes pubkey) path remains active.

Changes

Source (-48 lines)

• Distributor.sol: Remove MANAGER_ROLE, PECTRA11_HARD_FORK_TIMESTAMP, 5-arg distributeFor, admin functions. Add revert overrides for setZeroValidatorPubkeyGIndex/setProposerIndexGIndex to lock down unprotected base BeaconRootsHelper setters.
• IDistributor.sol: Remove 5-arg distributeFor declaration.

Tests (-523 lines, +128 lines)

• Migrate all tests to system-call path via vm.prank(SYSTEM_ADDRESS)
• Remove tests that exclusively tested the dead path
• Preserve all active-path coverage (system-call distribution, admin functions, upgradeability, reentrancy, dedicated emission streams, gas benchmarks, e2e fuzz)

Scripts / Mocks (-30 lines)

• Remove distributorManagerRole grants from deployment and ownership transfer scripts
• Simplify ReentrantERC20 mock to use system-call path

What was NOT removed (by design)

• BeaconRootsHelper.sol — retained because Distributor_V0.sol depends on it. Removing would break UUPS proxy storage layout.
• Storage variables — must remain at exact slots for proxy compatibility.

Security note

Removing the onlyRole(MANAGER_ROLE) overrides for setZeroValidatorPubkeyGIndex/setProposerIndexGIndex would have exposed these as unprotected public functions on the Distributor proxy (the base BeaconRootsHelper has no access control). While these values are only used by the removed verification functions (no direct impact on the active path), revert overrides were added to lock them down.

Verification

• forge build ✅ (clean)
• forge test ✅ (291 tests pass, 0 failures — includes 192 downstream RewardVault tests)

Diff stats

12 files changed, 153 insertions(+), 601 deletions(-)