Refactor and expand script verification tests

[stringintech]

Summary

Refactors script verification tests to use stateful object references (transaction, script pubkey, transaction output, precomputed tx data) instead of inline hex params.

Expands coverage from a single file to 11 dedicated files, one per output type (P2PKH, P2SH multisig, CLTV, CSV, P2SH-P2WPKH, P2SH-P2WSH, P2WPKH, P2WSH, P2TR keypath, P2TR scriptpath), each testing valid, corrupted, and flag-sensitivity variants (based on how I expanded the tests in sedited/rust-bitcoinkernel#137).

Adapts the dependency tracker to detect refs nested inside array-valued params, and documents the new/changed methods in handler-spec.md.

[stringintech]

Tested pre-release v0.0.3-alpha.4 in stringintech/go-bitcoinkernel#12 (comment).

[janb84]

ACK 66e1f3c

This was straightforward to implement and the extension of the test is welcome :)

2 suggestions:

(not related to the current changes) In the makefile L21, add build so that for a test no separate build command has to be given but only a make test will suffice :

Details

From:

	go build -o $(MOCK_HANDLER_BIN) ./cmd/mock-handler

test:
	@echo "Running runner unit tests..."

To

	go build -o $(MOCK_HANDLER_BIN) ./cmd/mock-handler

test: build
	@echo "Running runner unit tests..."

other nit see comment

[janb84]

NIT: suggesting to add test that shows that deep refs are not extracted, as per current contract

func TestExtractRefsFromParams(t *testing.T) {
	tests := []struct {
		description string
		params      string
		wantRefs    []string
	}{
		{
			description: "direct ref at top level",
			params:      `{"input": {"ref": "$ref_a"}}`,
			wantRefs:    []string{"$ref_a"},
		},
		{
			description: "refs inside array param",
			params:      `{"items": [{"ref": "$ref_a"}, {"ref": "$ref_b"}]}`,
			wantRefs:    []string{"$ref_a", "$ref_b"},
		},
		{
			description: "deeply nested ref inside array element is not extracted",
			params:      `{"items": [{"nested": {"ref": "$ref_a"}}]}`,
			wantRefs:    nil,
		},
		{
			description: "deeply nested ref in array is not extracted but direct ref alongside it is",
			params:      `{"direct": {"ref": "$ref_a"}, "items": [{"nested": {"ref": "$ref_b"}}]}`,
			wantRefs:    []string{"$ref_a"},
		},
		{
			description: "non-ref values in array are ignored",
			params:      `{"items": [{"ref": "$ref_a"}, "plain_string", 42]}`,
			wantRefs:    []string{"$ref_a"},
		},
		{
			description: "mixed direct and array refs",
			params:      `{"direct": {"ref": "$ref_a"}, "items": [{"ref": "$ref_b"}]}`,
			wantRefs:    []string{"$ref_a", "$ref_b"},
		},
	}

	for _, tt := range tests {
		t.Run(tt.description, func(t *testing.T) {
			got := extractRefsFromParams([]byte(tt.params))
			slices.Sort(got)
			wantSorted := slices.Clone(tt.wantRefs)
			slices.Sort(wantSorted)
			if !slices.Equal(got, wantSorted) {
				t.Errorf("extractRefsFromParams(%s) = %v, want %v", tt.params, got, tt.wantRefs)
			}
		})
	}
}