Delete reuse space

[lvca]

Pending PR to analyze differences after a long time working on this branch.

This PR is for #1391.

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
✅ +0.04%	✅ 86.45%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (a1716e9)	68118	43409	63.73%
Head commit (c0ba4ec)	68259 (+141)	43524 (+115)	63.76% (+0.04%)

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 (#1539)	214	185	86.45%

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%

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[lvca]

The main code is in LocalBucket.compressPage() which compress the page checking for holes created by record deletion. The compression is basically a shifting of the deleted record (hole) to the left. ArcadeDB page is separated in 2 parts: header and content. The header makes the RID and it contains the pointer to the actual record content. If the record is bigger than the space left in the page, then a multi-page record is created: basically the record is chunked and saved in next pages.

This PR is the first big step towards having 100% recyclable space. Once this is merged, there are still work to do to reach 100%. Here a brief summary of the TODO list:

• compress the LinkedList used for edges. New edges are added at the beginning (because the most typical use case is browsing from the latest). We have to come up with a compaction policy there too
• we need a way to reuse the space in the page instead of checking the space in the last page. At open time, we could easily have a quick scan of the first X pages of a bucket and save the information about how much space left is in each page. When the space is needed (new record, or update with a larger dimension), the deleted space will be reused based on convenience. For example, if a new record requires 5K of space, but the first 10 pages have less then 5K free, and the 11th page has 5K or more, the 11th page should be selected. This means the whole record can be on one page only