feat: rpc api key support with testnet readiness and performance improvements

[samclusker]

1. Fixes the observer crashing or hanging on Coston and Coston2, and corrects two bugs present on all chains.

Changes

ABI compatibility — Coston / Coston2

Coston and Coston2 have received upgraded VoterRegistry and FlareSystemsCalculator contracts
with a different event ABI from the stable Songbird/Flare versions. Added VoterRegistry_stable.json
and FlareSystemsCalculator_stable.json preserving the Songbird/Flare ABI and updated the upgraded
versions accordingly. Both sets of topic hashes are now registered at runtime so a single binary
handles all chains. VoterRegistered.from_dict updated to handle both the upgraded publicKey struct
and the stable flat fields.

Startup hang — Coston

get_unclaimed_rewards was making a lot of sequential RPC calls in a triple-nested loop, with
the contract object re-instantiated on every iteration - observed blocked startup on a busy RPC. Fixed by:

• Instantiating the contract once outside the loop
• Running all calls concurrently via asyncio.gather with a Semaphore(20) to avoid flooding the RPC
• Wrapping both call sites with a 60s timeout — the check is informational only and must never block startup

time.sleep in async context

Both polling loops used time.sleep(2) inside async def observer_loop, blocking the entire event
loop and preventing aiohttp from running connection cleanup. Replaced with await asyncio.sleep(2).

None medians — testnet only

On Coston/Coston2 some feeds occasionally receive no valid votes. The hard assert median is not None
is preserved on Songbird/Flare; on testnets a DEBUG log is emitted instead. Also fixed a latent
crash where an empty vote set would cause max() to raise on an empty sequence.

2. RPC API Key support

Added optional support for x-apikey to be used where needed.

3. Minor

• WTxData.wrapped: TxData was never read — removed to avoid holding tx objects in memory per voting round - maybe was a cause of high mem usage/OOMKilled observed.
• Descriptive KeyError raised immediately if the configured identity address is not in the signing policy
• Startup logging added for signing policy fetch and unclaimed rewards check

Feel free to cherry pick these changes as you see fit - also happy to just roll with my own fork but thought I'd share some findings. 👍