sstable: add code generator for sstable properties

[RaduBerinde]

The code to load/encode properties uses a mixture of relfection and
unsafe code and is fairly hard to understand. This commit switches to
using generated code instead. The generated code is straightforward to
understand.

Fixes #5098.

[cockroach-teamcity]

This change is 

[RaduBerinde]

Reviewable status: 0 of 20 files reviewed, 1 unresolved discussion (waiting on @jbowens)

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sstable/properties.go line 443 at r1 (raw file):

		p.saveUvarint(m, unsafe.Offsetof(p.RawPointTombstoneValueSize), p.RawPointTombstoneValueSize)
	}
	if p.NumRangeKeys() > 0 {

This conditional block is the source of the test differences: we no longer include these fields when the value is zero.

[RaduBerinde]

sstable/internal/genprops/gen_props.go line 1 at r1 (raw file):

// Copyright 2025 The LevelDB-Go and Pebble Authors. All rights reserved. Use

This was mostly written by o3 (https://chatgpt.com/share/e/687f9a51-6c38-8010-8c57-7682aecfea17). Feels strange to add this copyright to it, I'm not sure what the convention should be.

[petermattis]

Reviewable status: 0 of 20 files reviewed, 2 unresolved discussions (waiting on @jbowens and @RaduBerinde)

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sstable/internal/genprops/gen_props.go line 1 at r1 (raw file):

Previously, RaduBerinde wrote…

This was mostly written by o3 (https://chatgpt.com/share/e/687f9a51-6c38-8010-8c57-7682aecfea17). Feels strange to add this copyright to it, I'm not sure what the convention should be.

Let's leave this copyright header in place. Ack on the strangeness, but no copyright or some other copyright notice feels even stranger.

[RaduBerinde]

TODO: add a tag to allow interning of specific values like the merger name etc. Done