libbsdl: scaffold + working BSDL parser (struct + JSON, C ABI)

Standalone LGPL-2.1 parser for BSDL (IEEE 1149.1), shared by essim and
bs_explorer. The parser is ported from the Viveris JTAG Core loader,
decoupled from jtag_core, and extended with two extractions the original
lacks:
  - PIN_MAP_STRING -> per-port physical package pin, scalar and vector;
  - TAP_SCAN_*     -> TAP signal roles (TDI/TDO/TMS/TCK/TRST).

Exposes a stable C ABI (bsdl_parse_file/buffer -> bsdl_t, bsdl_to_json)
with a dependency-free JSON serializer and a bsdl2json CLI. CMake builds a
versioned shared library with install/export rules for find_package(bsdl).

Verified against m2gl010t, xcku040 and xcku15p (100% pin mapping, correct
IDCODEs and TAP roles); api and parse regression tests pass, clean build.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_api.c

@@ -0,0 +1,90 @@
+/*
+ * libbsdl - API test: exercises the lifecycle + JSON layer.
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "bsdl/bsdl.h"
+
+static int failures = 0;
+
+#define CHECK(cond) do {                                            \
+        if (!(cond)) {                                              \
+            fprintf(stderr, "FAIL %s:%d: %s\n", __FILE__, __LINE__, #cond); \
+            failures++;                                            \
+        }                                                          \
+    } while (0)
+
+int main(void)
+{
+    bsdl_opts_t opts;
+    bsdl_t model;
+    char* json;
+
+    /* version is reported and matches the compiled-in macro */
+    CHECK(bsdl_version() != NULL);
+    CHECK(strcmp(bsdl_version(), BSDL_VERSION_STRING) == 0);
+
+    /* defaults are sane */
+    bsdl_opts_default(&opts);
+    CHECK(opts.sort_pins_by_name == 0);
+    CHECK(opts.log == NULL);
+    CHECK(opts.log_user == NULL);
+
+    /* defined behaviour on bad input */
+    CHECK(bsdl_parse_file(NULL, &opts) == NULL);
+    CHECK(bsdl_parse_file("/nonexistent/does-not-exist.bsd", NULL) == NULL);
+    CHECK(bsdl_to_json(NULL) == NULL);
+    bsdl_free(NULL);            /* must be NULL-safe */
+    bsdl_string_free(NULL);     /* must be NULL-safe */
+
+    /* JSON layer over a hand-built model (independent of the parser) */
+    {
+        static bsdl_pin_t pins[1];
+        static bsdl_instr_t instrs[1];
+        memset(&model, 0, sizeof(model));
+        memset(pins, 0, sizeof(pins));
+        memset(instrs, 0, sizeof(instrs));
+
+        pins[0].name = "TCK";
+        pins[0].dir = BSDL_DIR_IN;
+        pins[0].physical_pin = "W20";
+        pins[0].tap_role = BSDL_TAP_TCK;
+        pins[0].in_bit = -1;
+        pins[0].out_bit = -1;
+        pins[0].ctrl_bit = -1;
+
+        instrs[0].name = "IDCODE";
+        instrs[0].opcode = "001001";
+
+        model.entity = "DEMO";
+        model.src_filename = "demo.bsd";
+        model.idcode = 0x12345678UL;
+        model.idcode_mask = 0xFFFFFFFFUL;
+        model.instruction_length = 6;
+        model.pins = pins;
+        model.pin_count = 1;
+        model.instructions = instrs;
+        model.instruction_count = 1;
+
+        json = bsdl_to_json(&model);
+        CHECK(json != NULL);
+        if (json) {
+            CHECK(strstr(json, "\"entity\":\"DEMO\"") != NULL);
+            CHECK(strstr(json, "\"physical_pin\":\"W20\"") != NULL);
+            CHECK(strstr(json, "\"tap_role\":\"tck\"") != NULL);
+            CHECK(strstr(json, "\"idcode\":\"0x12345678\"") != NULL);
+            CHECK(strstr(json, "\"name\":\"IDCODE\"") != NULL);
+            bsdl_string_free(json);
+        }
+    }
+
+    if (failures) {
+        fprintf(stderr, "%d check(s) failed\n", failures);
+        return 1;
+    }
+    printf("all API checks passed\n");
+    return 0;
+}