feat(twap-oracle): implement create_price_feed instruction

[0x-r4bbit]

Adds the CreatePriceObservations instruction to the TWAP oracle program.
The instruction initialises a PriceObservations PDA for a given price
source account and time window, writing the initial tick and timestamp
as the first entry.

Key design decisions:

• Per-window accounts: each (price_source, window_duration) pair maps to
  a distinct PriceObservations PDA. The window duration is baked into the
  PDA seed so a single price source can support multiple TWAP windows
  (24h, 7d, 30d) at independent sampling rates without sharing a buffer.

• window_duration not stored on struct: it is implicit in the PDA address.
  Any reader that located the account already knows the window duration
  used to derive it. Storing it would be redundant.

• Authorization is implicit: the PriceObservations PDA is derived from
  the price source account ID, so is_authorized = true on the price source
  proves the caller controls it without a redundant authority field.

• Impersonation is prevented by the PDA check: passing a controlled price
  source with a victim's observations account ID fails immediately because
  the computed PDA (from the attacker's source) does not match.

Closes #126

[Copilot]

Pull request overview

Implements TWAP oracle “price feed registration” by adding a CreatePriceFeed instruction that initializes a PriceObservations PDA for a given price source and records the initial tick + timestamp, replacing the prior no-op instruction.

Changes:

• Add CreatePriceFeed instruction in twap_oracle_core plus PriceObservations/ObservationEntry data model and PDA helpers.
• Implement program-side create_price_feed logic and expose it via the guest method entrypoint.
• Update dependencies, locks, and regenerated IDL artifacts accordingly.

Reviewed changes

Copilot reviewed 10 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
programs/twap_oracle/src/noop.rs	Removes the obsolete no-op instruction implementation.
programs/twap_oracle/src/lib.rs	Switches exported module from noop to create_price_feed.
programs/twap_oracle/src/create_price_feed.rs	Adds the instruction implementation and unit tests for initializing PriceObservations.
programs/twap_oracle/methods/guest/src/bin/twap_oracle.rs	Exposes the new create_price_feed instruction through the guest entrypoint.
programs/twap_oracle/methods/guest/Cargo.toml	Adds clock_core dependency for the guest build.
programs/twap_oracle/methods/guest/Cargo.lock	Locks clock_core and bumps transitive deps for the guest build.
programs/twap_oracle/core/src/lib.rs	Adds CreatePriceFeed, PriceObservations, ObservationEntry, capacity constant, and PDA derivation helpers.
programs/twap_oracle/core/Cargo.toml	Enables workspace lints and adds risc0-zkvm dependency used for PDA seed hashing.
programs/twap_oracle/Cargo.toml	Adds clock_core dependency and enables workspace lints for the program crate.
programs/token/methods/guest/Cargo.lock	Transitive dependency lockfile updates.
programs/stablecoin/methods/guest/Cargo.lock	Transitive dependency lockfile updates.
programs/ata/methods/guest/Cargo.lock	Transitive dependency lockfile updates.
programs/amm/methods/guest/Cargo.lock	Transitive dependency lockfile updates.
Cargo.lock	Workspace lockfile updates reflecting new/updated dependencies.
artifacts/twap_oracle-idl.json	Regenerated TWAP oracle IDL reflecting create_price_feed and new account/type definitions.
artifacts/stablecoin-idl.json	Regenerated stablecoin IDL reflecting newly visible types from twap_oracle_core.

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