solana-sdk: mirror ValidatorClientRewards as a zero-copy struct

[karl-dz]

Closes malbeclabs/doublezero#4183

Summary

solana-sdk

• Add ValidatorClientRewards as a Pod mirror of the onchain struct, with a PrecomputedDiscriminator impl, a Default impl matching the program's, a checked_short_description accessor, and a compile-time assertion pinning the account at 184 bytes
• Delete the five VCR_*_OFFSET constants, VCR_SHORT_DESCRIPTION_LEN, VCR_ACCOUNT_DATA_LEN, the standalone discriminator constant, parse_validator_client_rewards, and ValidatorClientRewardsInfo. None of them shipped, so the changelog bullet that introduced them is rewritten rather than paired with a removal entry
• Fold the new mirror into the existing mirrored-layout section alongside ShredRewardToken and ValidatorPublisherRewards rather than opening a second one

solana-cli

• Read the account through the mirror in show, claim, and init-holding. All three decode the whole struct, so they require at least the 184 bytes the program allocates
• claim takes its post-transaction count from SolanaConnection::try_fetch_zero_copy_data_with_commitment, which warns on a missing or undecodable account where the previous code printed (unavailable) silently

solana-fork

• Build the synthetic account from ValidatorClientRewards::default() plus field assignment instead of copying bytes to hand-written offsets, and size the rent exemption from the built buffer. The parse-back round trip and its three ensure! checks go with them, being tautological against a struct the same function builds
• Rename --synthetic-vcr-manager to --synthetic-validator-client-rewards-manager, along with the fork test script and the local-validator workflow
• That rename moves the environment variable clap derives from the flag, from SYNTHETIC_VCR_MANAGER to SYNTHETIC_VALIDATOR_CLIENT_REWARDS_MANAGER. A value left under the old name is ignored rather than rejected, so the fork boots with no synthetic account and the fork test fails later at the first validator-client-rewards show. The flag has only ever existed under ## [Unreleased], so no released version is affected, but anyone tracking main with the old name in a local .env or an infra job needs to move it

repo

• Record the conventions this change was written under in CLAUDE.md: the _key suffix for pubkey bindings, and which helper to reach for when reading a zero-copy account

Testing

• Unit tests across the three crates, including three cases for checked_short_description and an exact-match assertion pinning the rendered show summary byte for byte, which is what guards the format string's line continuations against a dropped escape
• The local-validator workflow drives show, init-holding, and claim against a synthetic account baked into the fork at genesis, covering the renamed flag and the mirror's field offsets end to end

[bgm-malbeclabs]

Checked the change against the onchain source rather than only reading the diff.

What checks out: the new ValidatorClientRewards mirror in crates/solana-sdk/src/shred_subscription/state.rs is field for field identical to the program struct in doublezero-shred-subscription, including _padding_0, _padding_1, _gap: StorageGap<2>, and #[repr(C, align(8))]. Size works out to 176, so 184 - DISCRIMINATOR_LEN holds and the offsets match the deleted VCR_*_OFFSET constants exactly. discriminator_slice() returns the same 8 bytes the old borsh::to_vec produced, so the synthetic fork account stays byte identical. cargo clippy --all-targets -- -Dclippy::all is clean on the three affected packages, unit tests pass including the exact match show summary assertion, and the \ line continuations in the new format! reproduce the old two space indent. No references to the deleted API remain.

No correctness bug found. One note below, not a blocker.