test: expose runner, archive, VFS, and SoftFloat regressions

[MuncleUscles]

Summary

Adds failing regression tests for 16 confirmed issues across runner metadata and rewriting, archive parsing, WASI/VFS mapping, Python calldata encoding, and SoftFloat integration.

This PR is intentionally test-only: it does not fix production behavior. The failing cases are collected here so the team can batch-fix them with clear reproduction coverage.

Regressions captured

• valid Wasm without an import section panics in the float rewriter
• non-function imports corrupt rewritten function indices
• runtime archive parsing rejects a valid USTAR form documented by the SDK
• USTAR prefix and name fields are joined without a slash
• full-width 100-byte USTAR names are truncated
• USTAR directory entries are exposed as files
• USTAR header checksums are not validated
• stored ZIP contents are accepted with an invalid CRC
• WASI parent traversal returns Noent because .. is discarded
• mapped paths containing . become inaccessible
• distinct archive paths that normalize to the same VFS path silently overwrite
• mapping a file over an existing directory silently deletes its subtree
• Python calldata encoding of memoryview produces an undecodable payload
• rewritten trapping float-to-integer conversions return saturated values instead of trapping
• runner metadata carrying the schema's supported $schema annotation is rejected
• unknown fields inside runner action payloads are silently ignored

Validation

• 75 unrelated executor tests pass
• formatting and structural checks pass
• a 31,000+ case scalar differential corpus plus SIMD coverage found no additional SoftFloat numerical mismatches
• each added regression test fails for its intended reason

Scope

• tests only
• no runner, executor, archive, VFS, SDK, or SoftFloat production changes

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