Use spec constants for PTC thresholds in fork choice

[dapplion]

Follow-up from #9025. The is_payload_timely and is_payload_data_available functions were using inline ptc_size() / 2 instead of the spec constant functions. This adds data_availability_timely_threshold() to EthSpec and uses both it and the existing payload_timely_threshold() in proto_array.

[eserilev]

@mergify requeue

[eserilev]

@mergify dequeue

[mergify]

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• -closed [📌 queue requirement]
• -conflict [📌 queue requirement]
• -draft [📌 queue requirement]
• any of [📌 queue -> configuration change requirements]:
  • -mergify-configuration-changed
  • check-success = Configuration changed
• any of [🔀 queue conditions]:
  • all of [📌 queue conditions of queue rule default]:
    • #approved-reviews-by >= 1
    • #approved-reviews-by >= 1 [🛡 GitHub branch protection]
    • #changes-requested-reviews-by = 0 [🛡 GitHub branch protection]
    • check-success=license/cla
    • check-success=target-branch-check
    • label!=do-not-merge

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-04-04 22:02 UTC · Rule: default
• ✅ Checks passed · on draft merge queue: embarking unstable (27af0ed) and #9088 together #9093
• ✅ Merged — 2026-04-04 22:36 UTC · at 346853683225a7416215fbcaeb15b201cd577244

This pull request spent 34 minutes in the queue, including 28 minutes 3 seconds running CI.

Required conditions to merge

• #approved-reviews-by >= 1 [🛡 GitHub branch protection]
  • Use spec constants for PTC thresholds in fork choice #9088
• #changes-requested-reviews-by = 0 [🛡 GitHub branch protection]
  • Use spec constants for PTC thresholds in fork choice #9088
• check-success=local-testnet-success
• check-success=test-suite-success

[mergify]

requeue

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