0.6.2: Shape inference errors "you forgot to specify hidden dimensions"; new notation `%%extend_dsls`

The notation %%extend_dsls generates boilerplate to add new operations to the DSLs -- making them easily available to the %op and %cd notations. It is for example used to add normal distribution to DSLs in a concise way.

Shape inference errors "you forgot to specify hidden dimensions" are generated when shape inference would otherwise need to guess the smallest fitting shape for a parameter.

From the changelog:

Added

• Normal distribution random number generation
• %%extend_dsls syntax extension for extending DSL modules
• interleave operation in DSL modules
• Defined_by_cd_logic shape inference specification for explicit shape logic in forward code
• Menhir-based einsum parser replacing Angstrom for better maintainability
• Name clash detection for inline definitions and variable captures in syntax extensions
• is_param flag in shape inference for improved parameter-related error messages
• Teacher forcing support in transformer implementation
• Heuristics for "missing hidden dimensions" error messages with row variables
• Tree_map persistent map utility with exposed tree structure in sexp serialization

Changed

• Migrated shape environment to use Utils.Tree_map for ppx_minidebug v3 full-scale debugging
• Replaced explicit non-iteration tracking with improved projection constraints derivation
• Support for offset-only affine expressions in shape inference
• Renamed optional dimension variable parameter from label to name
• Row IDs replaced with provenance tracking (Row.id → Row.prov) supporting deduplication
• Tensor labels interface improved: per-operation op_label string with label list as trailing parameter
• Adapted to ppx_minidebug renaming (entry_id → scope_id)
• Prefixed block names in lib/nn_blocks.ml for better namespace management
• Tests reorganized: more einsum-related tests moved to test/einsum/

Fixed

• Normal distribution test determinism across different machines
• Convolution/affine indexing shape inference offset adjustment by strides
• Parameter gradients not embedded after params moved earlier in processing
• Einsum parser handling of missing convolution and single-character cases
• Shape inference for Conv_input additional cases
• Incremental construction of tensors in Tensor.op
• Attention masks now have empty output dimensions for proper broadcasting to multihead attentions
• LUB (Least Upper Bound) computation in dim_ineq
• Axis labels distinguished from dimension units (labels) in shape_spec_to_dims_bio
• Shape inference for dim-1 with labels treated same as dim>1 (only dim-1 without label is different)
• Shape specification requiring LUB incorporation for non-terminal shapes
• Missing CUDA backend cases and NVRTC compatibility
• Premature guessing of dim variables as dim-1 when participating in Total_elems constraints
• Generic constraints ignored for unused tensors
• Missing propagation when set_dim happened before parsing the spec
• Guard axis_keys_to_idcs from un-inferred shapes
• More informative error messages for parameter shape errors
• Crash on repeated variable capture in syntax extensions
• Additional syntax support for binary einsum operators