Cardano Updates

v1 slices provided `.profiled` as an overlay rebuild with
`enableLibraryProfiling = true`.  v2 reads configure-args from
plan.json, so an overlay would emit `--enable-profiling` toggles
that plan-nix doesn't know about and the slice's UnitId would
diverge.

Replace the (missing) attribute with a `throw` that points users
at `cabal.project` / `cabalProjectLocal`:

    package <pkgname>
      profiling: True
      library-profiling: True

so plan-nix records the toggles and the slice's UnitId stays
aligned.  Set the `throw` at both the top level and inside
`passthru` because mkDerivation only lifts passthru → top level at
derivation creation time; post-hoc `// { passthru = ... }` doesn't
re-lift.

Adds `docs/dev/profiling.md` with the migration recipe.

Three incremental improvements toward making `lib/cover.nix` work
against v2 lib/test slices.  The end-to-end coverage test still
fails because v2's lib slices use a hashed UnitId
(`pkgb-0.1.0.0-<hash>`) while a sibling test slice rebuilds the
lib inplace and emits `.tix` referencing `pkgb-0.1.0.0-inplace`,
so HPC can't match them up.  That alignment is a deeper change;
land the supporting plumbing first:

  * Add `srcSubDir` / `srcSubDirPath` to v2 slice passthru so
    `lib/cover.nix:19`'s `map (l: l.srcSubDirPath) mixLibraries`
    no longer hits "attribute missing".

  * Library slices now copy each `extra-compilation-artifacts/hpc/<way>/{mix,tix}`
    subdir up to `$out/share/hpc/<way>/{mix,tix}/<pkg>-<ver>/`
    (the predictable name `lib/cover.nix` and the cover-report
    tests expect — v1 does this too in `comp-builder.nix:831`).

  * v2's `lib/check.nix` branch copies `<exeName>.tix` from the
    test run to `$out/share/hpc/vanilla/tix/<exeName>/`, mirroring
    v1's `lib/check.nix:119`.

Signed-off-by: Akhil Repala <[email protected]>

Signed-off-by: Akhil Repala <[email protected]>

The script ran a per-conf `diff -q` and a per-unit `diff -qr` on
every shell entry — for cardano-wallet's ~240 slices that meant
forking hundreds of `diff` invocations and walking each unit's
file tree.  Two short-circuits:

  * Per-composedStore marker file at
    `~/.cabal/store/.haskell-nix-shell-markers/<basename-of-src>`,
    written after a successful run.  On re-entry the marker is
    present and the script exits before the scan.  Different
    shells have distinct basenames, so alternating shells don't
    invalidate each other's markers.

  * Readlink fast-path in the scan: confs and lib files are
    installed as symlinks to `$src/...`, and unit dirs are lndir
    trees of symlinks under `$src/$ghcName/$unitId/`.  When the
    target is already in the right shape, skip the per-file `diff`
    fork.  Only when the cheap check fails does the script fall
    back to `diff -q` / `diff -qr` to detect genuine conflicts.

Measured on cardano-wallet's shell (~240 slices, fresh CABAL_DIR):
first run 24.5s, second run 0.012s.

The test runs `runghc conduit-test.hs` against `env.ghc` /
`envDefault.ghc`.  With v2's default
`exposePackagesVia = "cabal-store"` only `~/.cabal/store` is
seeded; plain `runghc` doesn't read the cabal store, so it failed
with "Could not find module 'Conduit'".  Switch the three shells
to `"ghc-pkg"` so `env.ghc` is wrapped to stack the composed
package.db via `GHC_ENVIRONMENT`.  Mirrors the earlier fix in
`tests.shell-for-setup-deps`.

- MempoolCapacityBytesOverride (See https://github.com/input-output-hk/ouroboros-leios/blob/ebc1f7c76b34e3d4f1b28485b720ed324633a6b3/demo/proto-devnet/config/config.yaml#L9)
- MempoolTimeoutCapacity