fix: bump policy-zig to v0.7.3

[jaronoff97]

Bumps policy_zig from v0.7.2 to v0.7.3 (release, usetero/policy-zig#103).

Upstream fixes:

• Contain allocation failures in matcher-index compilation (#99)
• Close build and fetch spans on their error paths (#101)

Test plan

• task signoff: lint, format, ReleaseSafe build, tests, s3-e2e.

🤖 Generated with Claude Code

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is an isolated policy-zig patch-version bump whose upstream changes are focused on allocation cleanup, error-path observability, and matcher edge-case correctness. It adds no new capability, schema, security, billing, or deployment behavior.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

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