feat: swap distribution metrics (Issue #2)

[Bigg770]

Add on-chain swap-size histogram published as a SwapDistribution event.

events.rs:

• SwapDistribution contracttype struct with four buckets: size_0_100 / size_100_1k / size_1k_10k / size_10k_plus + total_swaps.
• SWAP_COUNT_KEY and SWAP_BUCKETS_KEY instance-storage constants.
• Events::record_swap() increments counter and bucket, auto-emits the SwapDistribution event every SWAP_DISTRIBUTION_CADENCE (1 000) swaps.
• Events::emit_swap_distribution() for admin-triggered flush + bucket reset.
• Events::swap_count() helper for tests and analytics.

lib.rs:

• CounterContract::emit_swap_distribution() entry point (admin-gated).
• swap() now calls Events::record_swap() after every successful swap.

Also includes BatchShape optimisation (Issue #3) and its tests — both land in the same lib.rs file.

Tests (batch_tests.rs):

• test_swap_count_increments: asserts counter is 1 after one swap, 2 after two.
• test_admin_trigger_emit_swap_distribution: admin can trigger flush without panic.
• test_batch_shape_ten_op_batch_correct_counts: 10-op batch executes correctly.
• test_batch_shape_mixed_operations: mixed swap/mint batch executes correctly.

closes #91

[ameeribro4-sudo]

Nice piece of work on the swap distribution metrics — clean telemetry surface and the wiring into the existing events module is tidy. CI is green across the board. Merging 🚀

[ameeribro4-sudo]

Thanks again for the swap distribution metrics work — really nice surface 👋

Heads up: I went ahead and merged several earlier PRs (#101, #102, #103, and #110) before reaching yours. A few of those updated peerx-contracts/counter/src/lib.rs and the surrounding wiring, which now overlaps with your diff. CI was green when this PR was opened, but the merge into the current main now has conflicts.

Could you rebase this branch onto the latest main and push? Once CI re-runs green against the rebased tip, I'll merge it in. Happy to help if you hit anything gnarly during the rebase.

[ameeribro4-sudo]

@Bigg770 resollve conflicts please

[Bigg770]

@ameeribro4-sudo done sir can i be among the selected payers please