Reduce memory consumption when loading large number of commits

[stefanhaller]

(Github decided to auto-close #2533, and I don't see any way to reopen it, so opening a new one here. Please see there for discussion and review.)

When pressing > in the commits panel to trigger loading all the remaining commits past the initial 300, memory consumption is a pretty big problem for larger repositories.

The two main causes seem to be

1. the cell memory from rendering the entire list of commits into the gocui view
2. the pipe sets when git.log.showGraph is on

This PR addresses only the first of these problems, by not rendering the entire view, but only the visible portion of it. Since we already re-render the visible portion of the view on every layout call, this was relatively easy to do.

Below are some measurements for our repository at work (261.985 commits):

	master	this PR
without Graph	855 MB	360 MB
with Graph	3.1 GB	770 MB

And for the linux kernel repo (1.170.387 commits):

	master	this PR
without Graph	5.8 GB	1.2G
with Graph	Killed by the OS after it reached 86.9 GB	39.9 GB

The measurements were taken after scrolling all the way down in the list of commits. They have to be taken with a grain of salt, as memory consumption fluctuates quite a bit in ways that I find hard to make sense of.

As you can see, there's more work to do to reduce the memory usage for the graph, but for our repo at work this PR makes it usable already, which it wasn't really before.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 5a5cd841	✅ 75.61%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (5a5cd84)	Report Missing	Report Missing	Report Missing
Head commit (deee5fa)	52182	45140	86.50%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3687)	123	93	75.61%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

See your quality gate settings    Change summary preferences

---

_{🚀 Don’t miss a bit, follow what’s new on Codacy.}

_{Codacy stopped sending the deprecated coverage status on June 5th, 2024. Learn more}

Footnotes

1. Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct. ↩