d2b39e0 test: ensure old fee_estimate.dat not read on restart and flushed (ismaelsadeeq)
cf219f2 tx fees, policy: read stale fee estimates with a regtest-only option (ismaelsadeeq)
3eb241a tx fees, policy: do not read estimates of old fee_estimates.dat (ismaelsadeeq)
5b886f2 tx fees, policy: periodically flush fee estimates to fee_estimates.dat (ismaelsadeeq)

Pull request description:

  Fixes bitcoin#27555

  The issue arises when an old `fee_estimates.dat` file is sometimes read during initialization.
  Or after an unclean shutdown, the latest fee estimates are not flushed to `fee_estimates.dat`.
  If the fee estimates in the old file are old, they can cause transactions to become stuck in the mempool.
  This  PR ensures that nodes do not use stale estimates from the old file during initialization. If  `fee_estimates.dat`
  has not been updated for 60 hours or more, it is considered stale and will not be read during initialization. To avoid
  having old estimates, the `fee_estimates.dat` file will be flushed periodically every hour. As mentioned bitcoin#27555

  > "The immediate improvement would be to store fee estimates to disk once an hour or so to reduce the chance of having an old file. From there, this case could probably be detected, and refuse to serve estimates until we sync."

  In addition, I will follow-up PR to persist the `mempoolminfee` across restarts.

ACKs for top commit:
  willcl-ark:
    ACK d2b39e0
  instagibbs:
    reACK bitcoin@d2b39e0
  glozow:
    ACK d2b39e0. One nit if you follow up.

Tree-SHA512: 4f6e0c296995d0eea5cf80c6aefdd79b7295a6a0ba446f2166f32afc105fe4f831cfda1ad3abd13c5c752b4fbea982cf4b97eaeda2af1fd7184670d41edcfeec

This reduces chances of having old estimates in fee_estimates.dat.

Github-Pull: bitcoin#27622
Rebased-From: 5b886f2

Old fee estimates could cause transactions to become stuck in the
mempool. This commit prevents the node from using stale estimates
from an old file.

Github-Pull: bitcoin#27622
Rebased-From: 3eb241a

If -acceptstalefeeestimates option is passed stale fee estimates can now
be read when operating in regtest environments.

Additionally, this commit updates all declarations of the CBlockPolicyEstimator
class to include a the second constructor variable.

Github-Pull: bitcoin#27622
Rebased-From: cf219f2

This commit adds tests to ensure that old fee_estimates.dat files
are not read and that fee_estimates are periodically flushed to the
fee_estimates.dat file.

Additionaly it tests the -regtestonly option -acceptstalefeeestimates.

Github-Pull: bitcoin#27622
Rebased-From: d2b39e0

…` option is only supported on regtest chain

ee5a036 test: ensure acceptstalefeeestimates is supported only on regtest chain (ismaelsadeeq)
22d5d4b tx fees, policy: doc: update and delete unnecessary comment (ismaelsadeeq)

Pull request description:

  This PR Follow up comments from [#27622](bitcoin/bitcoin#27622)

  It test that the new `regtest-only` option `acceptstalefeeestimates` is not supported on [main, signet and test chains](https://github.com/bitcoin/bitcoin/pull/27622/files#r1235218268), removes an unnecessary [comment](https://github.com/bitcoin/bitcoin/pull/27622/files#r1235204323), and update fee estimator  `MAXFILEAGE` [description comment](https://github.com/bitcoin/bitcoin/pull/27622/files#r1233887314).

ACKs for top commit:
  jonatack:
    ACK ee5a036
  glozow:
    utACK ee5a036

Tree-SHA512: 4755f25b08db62f37614ea768272b12580ee0d481fb7fa339379901a6132c66828777c6747d3fe67490ceace3a6ff248bf13bdf65720f6e5ba8642eb762acd3c

… is only supported on regtest chain

ee5a036 test: ensure acceptstalefeeestimates is supported only on regtest chain (ismaelsadeeq)
22d5d4b tx fees, policy: doc: update and delete unnecessary comment (ismaelsadeeq)

Pull request description:

  This PR Follow up comments from [bitcoin#27622](bitcoin#27622)

  It test that the new `regtest-only` option `acceptstalefeeestimates` is not supported on [main, signet and test chains](https://github.com/bitcoin/bitcoin/pull/27622/files#r1235218268), removes an unnecessary [comment](https://github.com/bitcoin/bitcoin/pull/27622/files#r1235204323), and update fee estimator  `MAXFILEAGE` [description comment](https://github.com/bitcoin/bitcoin/pull/27622/files#r1233887314).

ACKs for top commit:
  jonatack:
    ACK ee5a036
  glozow:
    utACK ee5a036

Tree-SHA512: 4755f25b08db62f37614ea768272b12580ee0d481fb7fa339379901a6132c66828777c6747d3fe67490ceace3a6ff248bf13bdf65720f6e5ba8642eb762acd3c

This reduces chances of having old estimates in fee_estimates.dat.

Github-Pull: bitcoin#27622
Rebased-From: 5b886f2

Old fee estimates could cause transactions to become stuck in the
mempool. This commit prevents the node from using stale estimates
from an old file.

Github-Pull: bitcoin#27622
Rebased-From: 3eb241a

If -acceptstalefeeestimates option is passed stale fee estimates can now
be read when operating in regtest environments.

Additionally, this commit updates all declarations of the CBlockPolicyEstimator
class to include a the second constructor variable.

Github-Pull: bitcoin#27622
Rebased-From: cf219f2

This commit adds tests to ensure that old fee_estimates.dat files
are not read and that fee_estimates are periodically flushed to the
fee_estimates.dat file.

Additionaly it tests the -regtestonly option -acceptstalefeeestimates.

Github-Pull: bitcoin#27622
Rebased-From: d2b39e0

This reduces chances of having old estimates in fee_estimates.dat.

Github-Pull: bitcoin#27622
Rebased-From: 5b886f2

Old fee estimates could cause transactions to become stuck in the
mempool. This commit prevents the node from using stale estimates
from an old file.

Github-Pull: bitcoin#27622
Rebased-From: 3eb241a