feat: relax name validation and harden recovery

[zhourrr]

Relax document ID and collection name rules with centralized validation and clearer errors.

Fix related WAL recovery, schema, decoding, and Python/C binding issues while preserving storage formats.

Fixes #395

Validation Rules

The new rules are written as below, please review this first.

Identifier	Previous rules	New rules
Document ID	1–64 bytes; ASCII letters, digits, and _!@#$%+=.-	1–1024 bytes; valid UTF-8, excluding C0/C1 control characters, DEL, and Unicode line/paragraph separators (U+2028/U+2029)
Collection name	3–64 bytes; ASCII letters, digits, _, and -	1–256 bytes; same UTF-8 and character restrictions as document IDs
Field name	1–32 bytes; ASCII letters, digits, _, and -	1–64 bytes; same ASCII character set, excluding five reserved names: _zvec_row_id_, _zvec_g_doc_id_, _zvec_uid_, _zvec_score, and _zvec_group_id

Identifier Validation Performance

Summary

For valid ASCII inputs accepted by both implementations, the new validators were approximately 30–63× faster than the previous std::regex checks in this microbenchmark.

Valid Inputs Accepted by Both Implementations

Input	Previous (ns/call)	New (ns/call)	Speedup
Document ID, 8 ASCII bytes	674.91	14.70	45.91×
Document ID, 32 ASCII bytes	2,041.66	59.98	34.04×
Document ID, 64 ASCII bytes	3,563.33	110.87	32.14×
Collection name, 8 ASCII bytes	551.01	14.50	38.00×
Collection name, 32 ASCII bytes	1,796.46	60.26	29.81×
Collection name, 64 ASCII bytes	3,335.49	111.10	30.02×
Field name, 8 ASCII bytes	653.86	11.68	55.98×
Field name, 16 ASCII bytes	1,101.34	17.40	63.30×
Field name, 32 ASCII bytes	1,824.54	28.75	63.46×

Newly Supported Inputs

These inputs were rejected by the previous implementation. Only the new validation cost is reported, since the two implementations perform different work.

Input	New (ns/call)
Document ID, 256 ASCII bytes	420.46
Document ID, 1,024 ASCII bytes	1,793.87
Collection name, 256 ASCII bytes	436.82
Field name, 64 ASCII bytes	50.99
Document ID, 28-byte mixed Unicode input	42.13
Collection name, 28-byte mixed Unicode input	41.04