generate-accessors: annotation style + lifecycle generation

[martin-belanger]

This PR is a two-patch rework of the accessor generator, split from the earlier generate-lifecycle branch per reviewer's request for smaller incremental patches (see earlier PR: #3283).

Patch 1 — Switch annotations to // comment style

Replaces the /*!annotation*/ block-comment style with // !annotation line comments. The canonical form is // !token (one space between // and !). The parser accepts any amount of whitespace between // and !, so //!token, // !token, and //\t!token are all equivalent — making annotations resilient to contributor variation.

Updates all annotated structs in private.h and private-fabrics.h, and updates the documentation and helper scripts. The generated accessors.{h,c} and accessors-fabrics.{h,c} are unchanged by this patch.

Patch 2 — Add lifecycle and default-value generation

Extends the generator with two new annotations:

• // !generate-lifecycle (on a struct brace) — generates _new(), _free(), and (when defaults exist) _init_defaults()
• // !default:<value> (on a member line) — sets the initial value of that member in _init_defaults()

Applies // !generate-lifecycle to struct libnvmf_discovery_args, replacing the hand-written libnvmf_discovery_args_create() / _free() pair:

• libnvmf_discovery_args_new() replaces libnvmf_discovery_args_create() — same int return / double-pointer signature; sets defaults via libnvmf_discovery_args_init_defaults()
• libnvmf_discovery_args_free() is now generated (same name, same semantics — NULL-safe via free(NULL))
• libnvmf_discovery_args_init_defaults() is new; sets max_retries = 6 and lsp = NVMF_LOG_DISC_LSP_NONE

Updates all callers (nvme.i, discover-loop.c, test/ioctl/discovery.c) to use the new _new() API. Moves the ABI entries for the removed functions from libnvmf.ld to accessors-fabrics.ld.

Note on _create → _new renaming

A patch 3 to rename remaining _create functions to _new was considered but dropped. The _new suffix generated here carries a specific contract: allocate a zeroed struct on the heap, set default field values, and return it via a double-pointer with no other parameters. The remaining _create functions in the public API (libnvme_create_global_ctx, libnvme_create_raw_secret, libnvmf_context_create, libnvmf_create_ctrl) are fundamentally different — they accept multiple parameters and perform substantial initialization logic beyond just setting defaults. Renaming them to _new would misrepresent what they do and break the semantic contract that _new is meant to convey.

[igaw]

Thanks!