gh-151949: Fix Sphinx reference warnings in Doc/library/lzma.rst

The lzma module constants (FORMAT_*, CHECK_*, PRESET_*, FILTER_*, MODE_*
and MF_*) were referenced with the :const: role throughout the module
documentation but were never defined as reference targets, producing
"reference target not found" warnings under nitpicky mode.

Document these public constants with .. data:: directives, following the
convention used by the signal, socket and ssl modules, so the existing
references resolve. The now-redundant inline descriptions of the format
and check constants are condensed into linked references.

Author: fedonman

Doc/library/lzma.rst

@@ -152,35 +152,14 @@ Compressing and decompressing data in memory
    :func:`compress`.
 
    The *format* argument specifies what container format should be used.
-   Possible values are:
-
-   * :const:`FORMAT_XZ`: The ``.xz`` container format.
-      This is the default format.
-
-   * :const:`FORMAT_ALONE`: The legacy ``.lzma`` container format.
-      This format is more limited than ``.xz`` -- it does not support integrity
-      checks or multiple filters.
-
-   * :const:`FORMAT_RAW`: A raw data stream, not using any container format.
-      This format specifier does not support integrity checks, and requires that
-      you always specify a custom filter chain (for both compression and
-      decompression). Additionally, data compressed in this manner cannot be
-      decompressed using :const:`FORMAT_AUTO` (see :class:`LZMADecompressor`).
+   Possible values are :const:`FORMAT_XZ` (the default),
+   :const:`FORMAT_ALONE` and :const:`FORMAT_RAW`.
 
    The *check* argument specifies the type of integrity check to include in the
    compressed data. This check is used when decompressing, to ensure that the
-   data has not been corrupted. Possible values are:
-
-   * :const:`CHECK_NONE`: No integrity check.
-     This is the default (and the only acceptable value) for
-     :const:`FORMAT_ALONE` and :const:`FORMAT_RAW`.
-
-   * :const:`CHECK_CRC32`: 32-bit Cyclic Redundancy Check.
-
-   * :const:`CHECK_CRC64`: 64-bit Cyclic Redundancy Check.
-     This is the default for :const:`FORMAT_XZ`.
-
-   * :const:`CHECK_SHA256`: 256-bit Secure Hash Algorithm.
+   data has not been corrupted. Possible values are :const:`CHECK_NONE`,
+   :const:`CHECK_CRC32`, :const:`CHECK_CRC64` (the default for
+   :const:`FORMAT_XZ`) and :const:`CHECK_SHA256`.
 
    If the specified check is not supported, an :class:`LZMAError` is raised.
 
@@ -412,6 +391,106 @@ These filters support one option, ``start_offset``. This specifies the address
 that should be mapped to the beginning of the input data. The default is 0.
 
 
+Constants
+---------
+
+The following module-level constants are provided for use as the *format*,
+*check*, *preset* and *filters* arguments of the classes and functions above.
+
+Container formats:
+
+.. data:: FORMAT_XZ
+
+   The ``.xz`` container format.
+
+.. data:: FORMAT_ALONE
+
+   The legacy ``.lzma`` container format.  This format is more limited than
+   ``.xz`` -- it does not support integrity checks or multiple filters.
+
+.. data:: FORMAT_RAW
+
+   A raw data stream, not using any container format.  This format specifier
+   does not support integrity checks, and requires that you always specify a
+   custom filter chain (for both compression and decompression).  Additionally,
+   data compressed in this manner cannot be decompressed using
+   :const:`FORMAT_AUTO`.
+
+.. data:: FORMAT_AUTO
+
+   Used for decompression only.  The container format is detected
+   automatically, so that both ``.xz`` and ``.lzma`` files can be decompressed.
+
+Integrity checks:
+
+.. data:: CHECK_NONE
+
+   No integrity check.  This is the default (and the only acceptable value) for
+   :const:`FORMAT_ALONE` and :const:`FORMAT_RAW`.
+
+.. data:: CHECK_CRC32
+
+   A 32-bit Cyclic Redundancy Check.
+
+.. data:: CHECK_CRC64
+
+   A 64-bit Cyclic Redundancy Check.  This is the default for
+   :const:`FORMAT_XZ`.
+
+.. data:: CHECK_SHA256
+
+   A 256-bit Secure Hash Algorithm.
+
+.. data:: CHECK_UNKNOWN
+
+   The integrity check used by a stream could not yet be determined.  This may
+   be the value of the :attr:`LZMADecompressor.check` attribute until enough of
+   the input has been decoded.
+
+.. data:: CHECK_ID_MAX
+
+   The largest supported integrity-check ID.
+
+Compression presets:
+
+.. data:: PRESET_DEFAULT
+
+   The default compression preset, equivalent to preset level ``6``.
+
+.. data:: PRESET_EXTREME
+
+   A flag that may be bitwise OR-ed with a preset level (``0`` to ``9``) to
+   select a slower but more thorough variant of that preset.
+
+Filter IDs and options:
+
+.. data:: FILTER_LZMA1
+          FILTER_LZMA2
+
+   The LZMA1 and LZMA2 compression filters.  :const:`FILTER_LZMA1` is for use
+   with :const:`FORMAT_ALONE`, while :const:`FILTER_LZMA2` is for use with
+   :const:`FORMAT_XZ` and :const:`FORMAT_RAW`.
+
+.. data:: FILTER_DELTA
+
+   The delta filter.
+
+.. data:: MODE_FAST
+          MODE_NORMAL
+
+   Compression modes that may be used as the ``mode`` option of a filter
+   specifier (see :ref:`filter-chain-specs`).
+
+.. data:: MF_HC3
+          MF_HC4
+          MF_BT2
+          MF_BT3
+          MF_BT4
+
+   Match finders that may be used as the ``mf`` option of a filter specifier
+   (see :ref:`filter-chain-specs`).
+
+
 Examples
 --------