fix(perf): make provider budget gates constant time

[seonghobae]

Refs #814

Remediates the actionable post-merge review finding on #813.

Outcome

• reads the ADR 0014 synchronized incremental meter in budget_status()
• avoids deep-copying and rescanning up to 128 workflow runs before each provider call
• preserves buyer-facing spend aggregates, cost rounding, durable checkpoints, and fail-closed limit semantics
• proves the enforcement path cannot call spend_analytics()

Verification

• 1,727 tests passed on base 5b43ebfa77fa4a9f0feb2d0c414482dac1139bfa
• changed production statement/branch coverage: 100%
• orchestrator.py docstring coverage: 100%
• focused budget/generated/passthrough tests: 66 passed
• diff check and CodeGraph sync: passed

The pre-existing repository-wide coverage baseline is 92%, tracked separately in #815; this PR does not weaken or hide that denominator.

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[devin-ai-integration]

Devin Review found 1 potential issue.