chore: format cleanup to mach skill

[octalide]

Closes #362.

Brings every tracked .mach file into conformance with the mach authoring skill. Formatting, docs, and comments only, no semantic changes.

Changes

• Docstrings: converted all old-form # name: summary. docstrings to the new bare form (lowercase summary, no leading identifier, no trailing period); component # --- blocks preserved. Relocated two misplaced module docstrings (text/parse, memory) to the top of their files and added module docstrings to the four surface files that lacked one (lib, runtime/linux, runtime/darwin, runtime/windows).
• Alignment: aligned value columns in drifted rec/uni field blocks (sha256/sha512 State, darwin stat_t/dirent64, windows WIN32_FIND_DATAA) and use alias groups (toml, format, dns, rand, thread, parse).
• Indentation: converted the one tab-indented file (types/size) to 4-space.
• Naming: renamed the two convention outliers, internal spawn_ctx → SpawnCtx and the base64 lookup tables std_table/url_table/decode_table → STD_TABLE/URL_TABLE/DECODE_TABLE. Preserved the intentional lowercase primitive aliases (usize, isize, bool, char, str), libc/Win32 struct mirrors (timespec, stat_t, dirent64, ...), C stream names (stdin/stdout/stderr), and all ext fun symbol names.
• Em dashes: removed all 48 em dashes from comments (replaced with commas).
• Typo: fixed a pre-existing garbled docstring (timespe# → timespec) and a misattached docstring on the private cmp_ratio_pow2 helper in text/parse.

Committed in batches by directory. mach build . and mach test . pass identically (620 tests, 0 failures).

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