Point the finance examples' oracle path at Pyth and rename the mock feed

[mikemaccana]

The oracle network that the lending, perpetual futures and prop AMM examples modeled their price feeds on is shutting down. Every implementation is deprecated, support ends on 25 September 2026, and users are told to migrate to other providers. The examples still named it in 57 files, and their production-path comments told readers to build on it. After this PR, git grep -i for its name returns nothing.

The mock oracle is renamed

• The perpetual futures and prop AMM mock program is now mock-price-feed (library mock_price_feed) in both Anchor v2 and Anchor v1. The prop AMM's Anchor v2 package is mock_price_feed_prop_amm, for the same lockfile reason as before.
• The program ID, instructions, MockFeed account name and byte layout are unchanged. The programs' offset readers and the tests' instruction data are the same as before.
• The crate directory, the Anchor.toml key, the .so the tests load, the root workspace exclusion and the two root Cargo.lock entries change to the new name.

The production path now points at Pyth

• Every oracle reader comment, README, TERMINOLOGY.md entry and doc comment now describes reading a Pyth PriceUpdateV2 account owned by the Pyth Receiver program. The basics/pyth example already reads one.
• The lending README no longer says the old network was chosen over Pyth for compute cost. It now maps PriceUpdateV2 fields onto PriceFeed.
• Older changelog lines that named the network are reworded. New dated entries are in the root changelog and all nine example variants.

Verification

The container could not reach the Solana installer, so anchor build and the LiteSVM runs are left to this PR's CI. Locally I checked:

• cargo test --no-run compiles the Anchor v2 lending, perpetual futures and prop AMM programs, both mocks, and every test target. The build used empty placeholder .so files so the tests' include_bytes! resolves.
• The same command compiles all three anchor-v1 workspaces and their tests.
• cargo check --tests passes for all three Quasar variants.
• rustfmt --check is clean on every changed Rust file, except finance/lending/anchor-v1. There rustfmt flags lines this PR does not touch, and those were unformatted on main already.

Not in this PR

Cargo.lock on main is already missing a solana-clock dependency for betting-market, so cargo --locked fails on main as it is. That is unrelated to this PR, so I restored the lockfile to change only the renamed entries.

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https://claude.ai/code/session_01Bb9YgXxuvSJThr3TjtDoca

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