fix(cache): raise cache preallocation limit

[wan9chi]

Motivation

Automatically tracked task inputs are serialized as wincode sequences. Large real-world input sets can exceed wincode's default 4 MiB preallocation guard even when the cache payload is valid, causing cache reads and writes to fail.

Changes

• Give the persistent task-cache codec a 256 MiB preallocation limit.
• Centralize the cache-specific wincode configuration across cache reads, writes, and listing.
• Require each SQLite cache BLOB to contain exactly one encoded value.
• Bump the cache schema directory to v18 so the exact decoder does not open older rows.
• Keep the default guard for other wincode consumers, including IPC.

Fixes #557

[wan9chi]

• test(cache): cover large and unreadable entries #556
• fix(cache): recover unreadable cache rows #555
• fix(cache): raise cache preallocation limit #554 👈 (View in Graphite)
• main

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